Constantly keeping the battery at 100% can be an issue, but modern versions of macOS allow you to limit charging. There are also utilities that work on older OS versions (they just issue an SMC command to achieve the same thing), like this one: https://github.com/zackelia/bclm

I did this for a bit. The main issue was that air intake on my older model was through the keyboard, so clamshell mode was inadvisable - not sure if that’s true of the newer models and M1 should run cooler.

If you’re wiping it and installing Linux it’s like any other server, but if you’re running macOS you’re open to a wider spectrum of vulnerabilities that wouldn’t normally apply (desktop software). Your apps could also have vulnerabilities that expose access to personal credentials, etc (e.g. filesystems, apple id) depending on your setup.

You can insulate yourself a bit with tunnels/proxies to expose specific services (e.g. cloudflare, ngrok).

I had a lot more peace of mind buying an old, cheap computer, raspberry pis, and eventually NUCs.