Hmm I really like the idea of trying out a caster with a shield. Think it would be worth it to give him a caster a couple STR so he can equip some pieces of tank armor as well? Would it impede movement too much?
And it's good to know I can interchange 1h & 2h during combat. That definitely will give me a reason to collect 2h weapons now.
Right now I am using a Lonewolf sword/board warrior with water spells, a ranger with geo/witchcraft(maybe scoundrel later), and jahan + fire spells. My warrior is a beast but CC can really turn the tides when he's out front within range of every CC. After reading forums I already have some amazing ideas for my next party!
Level 7 on first playthru - have read all content lovingly and still feel lost - loving it 
I made a post on countering/avoiding disabling effects -
http://www.reddit.com/r/DivinityOri..._handling_disabling_effects_please_feel/As for giving a caster a shield, you'll need enough strength to wield a decent shield that you may as well get added protection from plate. Personally I prefer stacking int to max before putting points in anything else on my mages though. Mobility isn't really too much of an issue considering the combined mobility of man-at-arms gap closers and mage teleports that can bring enemies toward you if needed.
That said, Man-at-Arms and the magic abilities have a lot of synergy. You could pull off a hybrid if you choose wisely on your attribute split and talents. I'd focus more toward one thing than the other in the early-mid game though, and hybridize later in the game when you have more attributes to spare.
