Hi,
I think you should keep trying with the capsule, and find out exactly why it behaves strangely. for example, can isolate the player ina simple scene, and then see how it performs, maybe your props colliders are not set up properly. Play with physics material values to make them completly smooth and "icy" this is maybe the issue here. Capsule collider is used in most games, so it's definitly something to keep working on to get it right.
also, have you studied frameworks? there are a lot fo stuff on 2.5d type of game on the asset store.
bye,
Jean