Not amateurish at all, but good questions. I’m not confident enough to answer your second question, but on your first question: yes, you can use the hosting service you already have. Given that you are renting a VPS that is. It looks like Strato is calling this “hosting”. Don’t use their “WordPress hosting” package for this though, as it won’t allow you to install the instance software.

Controversial opinion maybe, but: pay for your apps/subscriptions. The makers need to feed their families as well. If you don’t want to pay big corporate, or the app doesn’t offer an ad-free alternative, switch to an indie alternative instead. If you can, pay for a lifetime plan.