Ok some quick tips...

It is possible to elminate portugal in three turns! When i started as the moors i sent an army to the oporto province. I can't remember why exactly but i didn't declare war straight away, but waited till turn 3. I besieged their main city and was then attacked by the main portuguse force. During the battle i killed all the General's bodyguards, next turn i was greeted by the fact that portugal was destroyed.

I haven't tested it again, but this does mean that sometimes it will be possible to eliminate portugal with one battle.

Other advice, is to take iberia asap. It shouldn't be overly difficult, my advice would be too take out portugal first, then the rebel provinces (though not valencia, leave that and el cid till after the spanish are dealt with). Then the spanish, it shouldn't take too long, after that you are practically homefree.