@
larsbb Good for you for seeing the build through to a completed bike!
You have 10 posts now, so you have to post a picture of the bike, or it doesn't exist!
Sorry for the push-back, but we see a lot of "I want to Build A Bike" threads where they don't want to spend any money, or have a pile of parts that don't work together (like MTB wheels on a TT frame) or want BF members to give them a complete shopping list, or they want something that really doesn't exist.
Saying you're a noob and asking about belt drives kinda raised that flag. BF is primarily a US forum, and belt drives aren't really common here.
You seem to have better than typical mechanical ability, and I'm glad you took this as a learning experience. As you found out, even simple bikes like yours are more complicated than they look.