AndersRickne: If i want to use magic in combat, how can i do this in the simplest way possible?
Press I during combat to call the inventory screen (it will pause the action). Browse the spellbook and cast the spell. I suggest to put the spellbook in the slot above the weapon one so you don't have to look for it in the backpack.
Alternatevely you can 'wield' the spellbook as primary weapon. When in combat doubleclicking a target should cast the spell 'bookmarked' in the book.
I suggest the first method above.
Besides buffs, cures, and the 'utility' spells, I don't think you'll need to cast offensive damage spells much. Well, you could if you want, but it's definitely not necessary given how the combat works.
AndersRickne: When i have the deed to the golden ankh, how do i use the deed to get the ship? I don't get a conversation option for it and i can't give it to clint.
I think having the deed in the inventory is enough, you shouldn't 'use' it explicitly. To use the ship doubleclick on the rolled sail. The party should automatically take seats, and you can control the ship. Doubleclick on the sail again to roll it and move the characters. To descend the ship doubleclick on one of the 'bridges' on the side to lower it.
AndersRickne: How many followers do i have and is experience points divided up among them so it's better to have fewer because you get more experience points per follower?
The max party size is 8 (the avatar and 7 companions). Some npcs wont join if there are already a certain number of members (simply tell some of them to wait, recruit the new one, and recruit those again)
Regarding XP, I think 'quest' xp is given to all party members (not divided, everyone is rewarded the same amount of points independent of party size, so party size doesn't factor in it).
In previous Ultimas 'killing' xp is give to the one who struck the final blow. I'm not sure about U7 but I think it's the same.
Most of your xp will come from doing quest. So I suggest to go with a full party.