I selfhost on a cheap VPS I found on LowEndBox. The security setup (not SimpleLogin) was more involved than SimpleLogin. Pretty easy to get working and I’ve had not a single issue in 1.5 years of selfhosting it. I pay $11/yr for the VPS compared to $30/yr for SimpleLogin.

With regard to your specific questions - I’ve only selfhosted for myself with one domain. You can add multiple users and domains though.

If you mean the gold guy on the horse when you first start, don’t fight him (yet). You can avoid him.

If you mean the first actual boss in the castle, you can get help from an npc or other players by using an item to see their “signs” on the ground and inviting them to your game.