As a self taught self-hosting enthusiast i wouldn't recommend ansible to a beginner. I know that sounds backwards as absible makes everything easy and does all the work for you but that's also part of the problem. It would be like jumping behind the wheel of a self driving car without knowing how to drive at all. When (not if) something goes wrong it could go wrong hard and you'd lose the whole instance.

It's better to start with some other self hosted projects that interest you to get a feel for the process and software like docker then work your way up to bigger things like lemmy. I consider myself fairly versed in the process and lemmy still gave me some issues to set up and my pixelfed instance still won't federate despite my best efforts. I'm pretty sure i know the issue, i just need to get around to fixing it.

Last thought, the raspberry pi is a pretty impressive little pc for it's size and price point but you might find yourself quickly burning through resources depending on the number of active users you have and how heavily you use it.