I'm in the market for an upgrade/new build with some parts coming over. My goal is to upgrade my current I7 7700k to a newer ryzen processor and motherboard. I'll probably need a new case as well. With the remaining parts I'm hoping to build a replacement for my current server (an old amd fx gaming PC). My budget isn't huge. maybe 400 usd give or take. I play at 1440p and I'm purchasing in the US.

my primary gaming PC has these components: 

I7 7700k cpu

Sapphire nitro+ 5700xt gpu

32gb (2x16) DDR 4 3200mhz (crucial i think) ram

z270 gigabyte motherboard

850 watt Corsair power supply

While my current system isn't too bad, the processor and motherboard are nearing 10 years old and lack 2 features that feel like big upgrades, Rebar and gen 4 pcie or higher. I keep seeing reasonable bundles over at micro center and I'm lucky enough to live near one. But I'm a bit unsure about which direction to go in the current climate.

On one hand going am5 with ddr5 ram looks possible with some bundles including mid range x3d cpus like the ryzen 5 7600x3d in my price range. unfortunately these bundles usually come with 16gb of ram, which feels like a downgrade even if it's faster.

on the other hand i also see some am4 bundles that feature cpus like a ryzen 7 5800xt for a little cheaper that come with 16 gigs of ddr4. This would allow me to bring my current ram kit into the new build while pairing the 16gig kit with an old 16 gig kit for 32 gigs in each build. it would also keep a little closer to by budget with a new case.

Does anybody have an suggestions on which move feels right given the current RAM market? 

Am4 vs am5 for this upgrade