1. I'd suggest trying it and seeing. My Jahan at the moment has no points in strength but I would consider him somewhat a 'battlemage' as he has ridiculous CON and survivability (become air, shield, elemental absorption, water of life, and both the electric and water touch spells along with vampiric touch).

2. You can take KIA whenever you want, and you can get to 15 base +1 KIA. Well for a 'pure' caster I wouldn't take Picture Of Health (and also wouldn't worry about CON). I've avoided Glass Cannon completely because it seems a little broken (as in overpowered, not unfunctional). My 'pure' mage survives by not getting attacked (other things in the way/enemies cannot act due to CC) and has maybe 6 base CON.

3. Max for any stat is increasing its base (starts at 5) to 15. Some things give additions on top of this (like Know-It-All). I'm not sure how politician works, if it reduces after your base or from it.