I'll try as best as I can. in order asked or mentioned.
about 50% faster the 2070 is. results for the gist only, the general idea:
https://gpu.userbenchmark.com/Compare/Nvidia-RTX-2070-vs-Nvidia-GTX-1660/4029vs4038
1080, 1440 and 4 k are all resolutions the card needs to draw depending on the screen. the monitor you are using will determine the resolution. you would not want the GPU to render a 4k scene when your display can only ever display 1/4 of those pixels as is the case on 1080 which is exactly 1/4 the pixels of a 4k . by the same token you would not want to display a low resolution 1080p game on a 4k display. the GPU and the monitor need to be copacetic, working along the same lines.
I still play on 1080p, FWIW.
for the SSD's nowadays its your choice, when the drives were new and small, 64-240GB the limited space meant that you could ONLY put the OS and a few games on it. now 1tb drives are available and the size issue is not what it once was. I prefer a speedy largish (over 512GB) SSD and a huge HDD (3x3TB) for my storage needs. your needs will vary but if you can afford a 1TB SSD I suggest you go that route. SSD's have a couple varieties, SATA interface and M.2 interface. SATA drives are slow and some M.2 drives are SATA. the fastest m.2 SSD's have the term NVME attached, Non-Volitile Memory Express, NVMEs drive can be as much as 6 times faster than a SATA SSD, and SATA SSD's can be 3-4 times faster than a HDD. all that being said you are only going to notice the difference in speed an NVME drive gives over an SATA under certain workloads, for most daily driving tasks the SATA drives are fine for most people. when you have two NVME drives is where the speed really shines through and NVME struts its stuff, drive operations between NVME drives is a beautiful thing.
"what constitutes a weak Motherboard?" poor diet and lack of exercise.
seriously though any motherboard you consider should have the ports you will need, USB 3, PCIe slots, M.2 slots etc. the Voltage Regulation is of concern when heroic overclocking is involved, if you only intend to overclock the RAM, its not much of an issue, for CPU overclocking you want proper cooling on the VRM. the VRM is around the CPU socket and there should be some sort of a heatsink on these circuits before doing any CPU overclocking. if you wish to overclock the CPU I suggest a higher end chipset like the x570/550 for a third generation Ryzen CPU. get the latest generation you can on the CPU. if you get a third generation ryzen get a 5 series chipset based motherboard. if you get a 1 or 2 generation ryzen you can get a 4 series chipset based motherboard. the 4 series can take a 3rd gen ryzen, so there will be upgrade paths, the 5 series boards are new and SHOULD be able to upgrade to newer chips as they are released.
for a current CPU's the standard is DDR4 RAM. the CPU will dictate which RAM to use as the memory controller circuitry is embedded into the CPU. for the third series ryzen look to 3600Mhz ram or better. ryzen loves all the bandwidth you can give it. as to the GPU it will depend on your screen as described above. what is the resolution and refresh of your display? you will need a card that can happily handle that workload.
if you build a Rig you will need to buy windows (or run without a license until you can afford it) prebuilt systems will have windows installed already.
of you can turn a screwdriver you can assemble you own PC. a Phillips screwdriver, and some patience are all that is required. read the manuals, watch some assembly videos on YouTube to get the idea of what is involved and what goes where. the Forums and ambassadors like me are here to help with anything you may need. I do not like pre-built PC as they are built to a price point often containing substandard PSU's, crippled motherboards (features removed), etc.
the archangel units for example, I'm not a fan of that case. the front ventilation is hindered to look pretty. 80 plus bronze rated PSU, but which one? is it a good unit? will it need replacement in a month? the images also show that ONE RAM stick is installed, single channel memory will cripple the bandwidth that ryzen loves. to enable dual channel you need two matching sticks of RAM sold in a set for the best performance, you cannot simply add another stick and expect it to work like a matched set. the chassis is a full ATX case but the motherboard is mATX, three expansion slots are not usable. I would suggest a full ATX board a Full ATX case.
I hope this has been helpful and hoping you build yourself here is a few words on grouding I have prepared.
Assembly grounding:
plug in the power supply to the wall. you can touch an unpainted part of the PSU (insert an unpainted unfinished screw into the PSU mounting holes and touch the screw as a grounding point) once you have grounded yourself you can now touch and assemble the parts of the PC.
if you move your feet, or shuffle in your chair, reground yourself again.
install the CPU into the motherboard and the RAM into the slots.
if you move your feet, or shuffle in your chair, reground yourself again.
install the cooler to the CPU. install the motherboard into the case.
secure the motherboard down with the screws, make sure you remove any unwanted/needed mounts before securing the motherboard.
unplug the PSU and ground yourself again. install the PSU into the case and secure with the 4 mounting screws.
plug in the power cord and ground yourself again from now on after grounding, unplug the power supply cord from the wall.
if you move your feet, or shuffle in your chair, plug in the cord, reground yourself and unplug again.
connect the power supply to the motherboard by the 24 pin and the AUX CPU power connector, install the GPU if one is selected, and install the drives with the supplied mounts in the case. connect the front panel connections to the case according to the manuals.
if you move your feet, or shuffle in your chair, plug in the cord, reground yourself and unplug again.
if there are any other peripherals, like wifi cards or sound card install and secure now. verify all power cables are connected to the motherboard and the GPU if needed.
the system can now be booted and the BIOS adjusted if needed (refer to motherboard manual) then an OS installed. when you are sure the system will need no more working/tinkering you can install the side panel and close the case. you have now assembled a PC.
end canned rant