Where should i buy my domain and are there any things i should be careful about?
Just becareful about renewals. Sometimes a domain will be cheap year one, but crazy expensive year 2+. I personally use Porkbun
does the end of my domain (idk the specific name but .XYZ) matter at all?
Sometimes it can matter. If you host email, some TLDs are classed as higher risk and could be wholesale blocked or classed as higher risk.
Am i willing to self host too much stuff?
That's a question of how much time do you mind spending configuring, maintaining, and upgrading. I run way too many services. Some of them require more effort than others. Forgejo requires more effort to get working than Immich for me trying to get Forgejo Actions working well.