Homelab upgrade help

Currently running a homelab setup with an i7-4770, 2x 8GBs DDR3 @ 1600MTs and both an internal 1TB HDD for the OS and an external 3.6TB HDD. Running headless Debian 12 LTS.

I currently run Jellyfin, Immich, Crafty (minecraft), and Nginx.

I feel the need to upgrade but im not sure what to. I know I'd like to get an SSD to replace the 1TB drive, could even downscale to 256 or 512GBs, and that I'd probably be better off with DDR4, maybe even 32GBs rather than 16.

What would be the suggested option here? How much would this sort of upgrade cost?

Based in the uk if that helps/changes anything, literally just looking for an upgrade not the absolute best, and I'd prefer used (ie ebay, cex).