The 3700x is the best mixture of overall number of threads capability and single core performance, without venturing into "I'm going to need really capable cooling for this". Although, with the coolers you AND I had picked out, you could easily run a 3900x or 3950x as well. But you would be a lot more likely to encounter issues of a thermal nature regarding an inability to maintain boost clocks because those CPUs are simply going to have a higher TDP and nothing can be done about that. IF you were to choose one of those two higher end Ryzen 9 models, it would be advisable to also opt for a much higher end motherboard than what is probably necessary for the Ryzen 7 3700x. Factually however, if you could get something like the Tomahawk max (B450) or Gaming Pro Carbon, it would handle any of those CPUs. Suffice to say, there is really not a lot to be gained by going from the 3700x to a higher end CPU unless you NEED a high end desktop configuration because you are running extremely demanding professional applications AND compounding the demand on system resources by also doing some form of high level multitasking by running those applications and a bunch of other stuff, simultaneously.
For most people, even a fairly high level of multitasking is handled easily by the 3700x. If you didn't NEED to do this now, I'd say waiting for the Q4 release of the Ryzen 4000 series parts would be wiser, but honestly we don't even know what that is going to look like yet in terms of any performance improvements over 3000 series parts OR when exactly that is going to happen, so I don't advise that at this time.
The Corsair H150i is reliable, as is it's software. Others, are varying levels of "crap, why aren't these issues sorted out by now". I advise sticking to the more reliable, and highly customer service oriented Corsair in this case. And to be honest, the only reason I chose an AIO is because, you did, plus you made it clear that the goyl fiend wants pretty lights, so this gives you good performance, reliability AND pretty lights. You could probably get away with just a 280mm cooler, if you had to go with an AIO, but you've got room for a 360mm in front of that case, the other fan location wouldn't get used at all if you put a 280mm so it would be a waste, and it wouldn't look as good as with those three fans in front all RGB'd up. If you were inclined to let the AIO go and just put some regular RGB case fans there, I could definitely make air cooler recommendations which is probably what "I" would do, but I tend to stick with air cooled rigs anyhow. I don't care to put something in my case that can potentially leak and ruin other hardware, and yeah, it happens from time to time. Not very often, these days, but occasionally.
Either way, if you are going to go with an AIO, that is far from the worst choice you could make, it is more than enough cooler for that CPU, the price difference between that and a 280mm model is minor and it's got quite a few good reviews. If you don't like that cooler, there are definitely other options. The
Fractal Design Celsius+ S36 Prisma PWM ARGB is a good choice, but like a lot of things right now, it is significantly more expensive than it usually is currently.
B550 Steel legend. A solid, proven mid tiered model. Not particularly cheap, but good features, and right now, nothing is particularly cheap, so this is a good choice since it's got PCIe 4.0, 2.5GB LAN support (So 1.5x faster than most current Gigabit ethernet adapters, if you have a network or ISP connection that can benefit from it), dual M.2 slots that both support NVME drives and pretty much everything else you would want including addressable RGB headers. A CPU fan, water pump and five multi purpose (Fan or water pump) fan headers that all support both 4 pin PWM and 3 pin DC voltage controlled fans and pumps.
The Trident Z Neos are made for Ryzen 3000 series. This kit is not only as fast as you can get without paying a penalty at 3600mhz
without having the infinity fabric uncouple, it also not only has timings that are favorable to Ryzen because they are made for Ryzen, but also has pretty low timings overall with a 16-19-19-39 configuration. There are some Trident Z and Ripjaws, both of which I prefer for Ryzen because they seem to be a lot more generally compatible than kits from other brands, that are even lower 16-16-16, or even CL14 which are very fast, but they are a lot more expensive than you probably want to splurge on. Plus, these also have RGB, so, more pretty lights for the goyl fiend.
The Seagate Firecuda has a longer warranty and longer specification for TBW (Terrabytes written) than the Samsung 970 EVO Plus, which would have been my usual choice. The Firecuda has a slower maximum sequential write speed than the 970 EVO Plus, BUT, unless you are writing from M.2 to M.2 drive, and are writing large sequential single files, you are never going to see those kinds of speeds anyhow. Even then, it's theoretical, not real world. So not a big deal really and the read speeds are the same. What is important to me for a work machine is that this is a more reliable enterprise or high end desktop type device with a better TBW and better MTBF (Mean time between failure) to the tune of 1,800,000 hours compared to 1,500,000 hours, so 300,000 hours longer for less money.
It also has a marginally HIGHER random write speed than the 970 EVO Plus. And since random reads and writes are where most storage devices live, it's probably the more important specification than the headline grabbing sequential speeds.
The Ironwolf NAS, very solid, very reliable, enterprise type drive. I have a 16TB version of this drive. It is without doubt one of the most reliable drive options out there. With 6TB, you are going to have plenty of room for storing games, work files, music, documents, etc. It WOULD be VERY SMART to also get yourself either a second one of these OR some flavor of 6-10TB external drive for backing up recovery images of your Windows 10 installation and ALL important files that would normally be stored only on either the OS drive or the secondary 6TB drive, so that you don't end up like some of our stump heads back here crying about how a drive failed (Which it will, because all drives fail eventually or sometimes prematurely) and you didn't have any backups.
The graphics card I already covered pretty much, but suffice to say, unless you get a higher end EVGA card, I doubt anybody is going to advise you of a better quality card for the same price.
The Supernova G3 EVGA power supply is based on the Super Flower Leadex II platform, which itself is one of the better platforms out there across the board. The fact that it's under 150 bucks when everything else worthwhile seems to be much more right now, makes it even more compelling. For 150 bucks, if there is a better power supply in this category that you can ACTUALLY get your hands on and doesn't have 40-75 dollars worth of shipping charges attached to it, I'd like to see somebody point it out.
The Meshify S2, which is the latest version of the Fractal Design Define S, but with a full mesh front panel, allows the lighting from your AIO RGB fans to shine through, plus it offers full panel airflow with very little restriction. On top of that, it's Fractal design, which means it's a well respected, very high quality product with a level of customer support that is almost unmatched in the industry except for probably EVGA who is hands down the best company to deal with on any product support issues or warranty claims. This case is 100% designed for water cooling, so if you were to decide to go from an AIO to a custom loop at some point in the future, it's already ready for it. If not, it's still a very good choice for a system with a big AIO, with no obstructions in the air path from radiator to exhaust fan locations and a very clean internal design with good cable management features and a PSU shroud as well. Drives can be mounted either in the drive cage that comes able to be mounted in the bottom of the case OR on the backside of the motherboard tray, completely out of sight and out of the air path so they and their cables don't create obstructions.
Windows, is self explanatory. If you don't need it because you already have an eligible product that can be moved to this system, great, if not, you need it. What you don't need is the Pro version, because the differences are negligible unless you are an enterprise user or overtly anal retentive and just want the Pro version because "all your friends have it". It's pointless IMO unless you NEED the Bitlocker encryption, built in remote desktop, Hyper-V (Virtualbox is better, and free, so no need for this either) or want to be able to shut off Windows updates, which I HIGHLY recommend not doing unless you are running very old applications that have a tendency to break when Windows is updated.