Just sold my DS1515 what’s the smartest upgrade path?

Hi everyone,
I just sold my Synology NAS 1515 (not the + version), which I had upgraded to 8GB of RAM and filled with 4TB WD Red drives. I decided to sell it because I felt it was getting a bit old, and I got an offer I couldn’t refuse.

The 5 HDDs were configured with Synology’s proprietary filesystem.
Do you think it makes sense to go for the 4800 Plus, or would you recommend something else?

I’d like to start experimenting with Docker, since up until now I’ve been relying on external devices like various Raspberry Pis (for Pi-hole, etc.). My goal is to centralize everything in one system.

For now, the storage space is actually overkill for me — I’m only using about 10% of the whole pool.

My budget isn’t huge, so I’m looking for the best balance.
Thanks a lot for your advice, and sorry for my poor English!