Ok, sorry I didn't get back to you sooner but I was busy today replacing the power brake booster in my car and it was a real PITA. I do this professionally and I've rarely seen a brake booster require so much to be removed and such a complex procedure. That's what I get for driving a Mazda, and an older one at that, I guess.
So, anyhow, you need a motherboard, power supply, storage, and that's pretty much it since you already have a case, CPU and memory. However, the memory could be a problem so we will TRY to ensure we pick a motherboard that "works" with the memory kit you have but no promises there as that aspect can get complicated sometimes. Especially with Ryzen. ALL generations of Ryzen. Newer generations are much better but as always there can be issues with compatibility even as there is with Intel sometimes.
Probably also need a cooler and fans. The fans that come with that case are not sufficient for the entire build most likely and the stock CPU cooler, well, I wouldn't recommend it unless you enjoy listening to the CPU cooler fan ramp up, and down, and up, and down, and up, and, well, you annoyed yet? Because you will be with the stock cooler that is VERY "cyclic" and annoying. Get a better cooler and never have to deal with that kind of annoying cycling or harmonics.
Now, here is the thing. Really. Do you NEED this right away, or is it something you "could" wait just a bit for, and I ask for a good reason. That reason is that AMD is releasing new CPU's soon and the expectation is that it will be announced around the 30th and the new products will be available around the middle of September. Now, if you NEED something now, makes sense, and I never would tell somebody to not buy what they need IF they need it now. But both Intel and AMD are supposed to be releasing new products soon so what that likely does is
1. Either provide the potential for a bump in performance at or near the same price as what's available now.
2. Or, definitely offer the potential for better performance for less since ALL of the Ryzen processors from the upcoming release will have integrated graphics and you don't have to pay a premium for a lower core, lower performing SKU just to get graphics included.
3. We've never really seen Intel and AMD both release new products at the exact same time, so what this MIGHT do is create a heck of a competitive atmosphere where the buyer wins, for once.
If you really need to do something now, I'm happy to help, and I'm happy to help even if you're willing to wait and revisit it once the releases of new products happens, but I figure it was the best and most honest approach to let you know the reality of the situation so you could make that call yourself, as an informed decision.
And no worries, if you decide you want to wait and see what shakes out, I'm happy to stay with you on it and help guide you through that scenario if you choose to. Either way, it's all good.