I agree with Arjos that it can be a good idea to start with the Romani just to get a feel for it. I believe one of the more challenging aspects for the beginner is the economy, with which the Romani has an easy time. You won't be starting by recruiting a lot of troops and building barracks: you should focus on roads and markets. I haven't tried the Lusotannan, but I can imagine them having a tough start, getting easier. Iberia is a very rich region, but you will have to conquer it. Difficulty: M/M. Not so easy as to spoil you, not so hard as to make it ridiculous.