Frankly, If you want to play right now, and since RTX 3000 is there you can buy without worries, if you can contain yourself and wait 4000, it wont take much longer now, if you wanna have fun right now, we're still in september after all, go for it, you'll still be playing with attrocious amounts of fps with that card, so no worries at all for years to come.
I'd prefer 2x16 instead of 4x8, its likely that you''ll have to increase the command rate to 2t, theres small performance drop but its there, plus going all 4 , there might, just might be the need to loosen some timings a little bit, imo, i'd stick with the good old dual channel, specially on ryzen, they're a bit picky about ram, so you might want to check on corsair page if they are certified because some are just straightforward problematic with ryzen. other than that, either 3700 or 3900 are golden, you'd be covered core-wise.