Is /usr/local a per user folder?
No, /usr/local is not a per-user folder. It's the same directory for all users. I've been down this road with homebrew and done the chown to /usr/local on a laptop that only I use, but my other non-homebrew-aware Macs all show permissions similar to this for /usr/local:

%ls -ld /usr/local

drwxr-xr-x   213 root     wheel    578 Aug 28 11:58 /usr/local


And they work just fine like that.