Yes, of course you can use any amount of ram you wish (within the restrictions of the motherboard. The type of GPU makes no difference to the amount of system ram you can use.
In terms of speeding up the GPU, it doesn't make a difference in performance that much at all. It can however, make your CPU work faster, and supply the GPU with date more quickly, which can result in a slight increase in FPS. But as a direct link to the GPU faster system ram, doesn't impact that much at all.
Edit: 16gb is a good amount for a gaming system now. The 'Sweetspot'!
System memory is independent of the gpu.
A balanced build is usually the safest bet, so 8 gigs if you want to save a buck and upgrade later, or 16 if you want to comfortable (for most gaming related things)
The speed of your ram does matter for your gaming experience and fps, with 3200-3600 CL15-CL17 being the sweetspot.
Personally I do a lot on my computers at one time. My previous computer of 7 years had 16gb of RAM and that slowly became not enough for me. My newest system has 32gb of extremely overkill RAM (gskill 4x8 3600 14-15-15-35) and that is enough for me for now. I believe that today 16gb is the minimum amount of RAM for a gaming PC that has stuff going on in the background. 32gb is a luxury but not a hugely expensive one. In 1 year you will most likely be buying a PC with DDR5 RAM and I would recommend getting a 16gb kit to start and if that is not enough get a 32gb kit and return or sell the 16gb kit.
in my pcs I go for 32gb ram because games are starting to use more and more with Microsoft flight simulator using 16 gigs now, and with the new consoles having 16 gigs, games are going to be optimized to use almost up to that, and if you want to have discord and a few tabs and play games in the next few years, 32 gigs might be the best for you (if it is in your price range, 32 gigs can get expensive)
Today for gaming and arguably office work 8 GB of RAM is the minimum, 16 GB is the sweet spot, 32 GB is not needed for most of the users. 3200 Mhz is the sweet spot for RAM speed.
For VRAM 8 GB RAM is both the minimum and the sweet spot. Most games cannot make use of anymore VRAM (One exception is Flight Simulator), that means RTX 3080 and RTX 3090 performance identical in almost any game. But