Regarding having confidence in the Buddha's teachings on rebirth, nibanna, and all the central aspects of Buddhism, I think of it like this:
If I want proof before believing these things for myself, it is good enough for me if someone has died, taken rebirth, achieved liberation, and told us, "I've see this, I don't want it for you, and here's how you can stop it." If I wait to experience it for myself, I'll either be dead and taking another rebirth out of ignorance, or I'll be doubting nibanna for the next umpteen lives. So it is proof positive for me that somebody only a couple of thousand years ago experienced it and told us about it. Unless you think the Buddha was incoherent or kooky, he's etched out a fine path that we can follow.
My two cents
Edited to add: I know that many people don't like ritual and fancy Buddhist-stuffs. But I'll you that from my pov, people who struggle with parts of the Buddha's dhamma might find spending time daily really focusing on venerating the Buddha might be useful. I know I might make people mad by saying that, but it's just my opinion