Here's what id do whilst playing Spain

Expansion
Takes Zaragoza first, if possible siege attack it while the Portugeese are there too, extra men, weakening another army, and you get the settlement not them. I wouldnt take Valencia, not yet as it has a decent general, a decent garrison and barely anybody attacks it. Next i would try to take Moors out of Spain, and keep pushing them back, when i did this, i think the last settlement they had was Tunis, and they had garrisoned it with their last family member. Then i reccomend taking Bordeux, or Valencia, Pamplona and atlast Lisbon. Also you might think about taking Ajjacio and Cagliari, south of Genoa.

Trade and the Economy
Send a single diplomat or a princess to Central Italy, and watch as her charm increases rapidly as she is visited by a diplomat from nearly every faction on the game. As for economy, Ajjacio, Cagliari, Zaragoza, Valencia and Leon all prove as very good trading cities, aswell as providing a good income.

Papal Favour
I suggest participating in a crusade, and walking down through Africa, sacking every settlement you come across, giving it to the Pope, or you could exterminate them and keep them, giving the crusade target to the pope.

Problems
Being surronded by enemies. Portugal will ally with France and Moors and will try to throw you out of Spain. Dont let this small insignificant faction plot against you, destroy them with the first chance you get. I suggest killing Moors next, France may attack you first, but if you kill Moors, i guarantee that Egypt is not bold enough to cross the desert and hit your rear, so they you can focus on killing France

Well i hope this helps in your campaigns as Spain