I need to go soon, so my reply will be short but I will get back to this, later tonight.
You can have 1 summon per character, to a total of four summons. I got the idea you took you can only have 1 summon to literal.
And you basicly want glass cannon on each character, it is the uncontested best talent this game has to offer. (save your talent @ level 3 and use it @ level 5 to take up glass cannon.)
As far as battlemage/mage is concerned, both are great casters, a pure mage however will have more schools maxed while the battle mage probably has 1 caster school maxed.
Sadly have to be somehwere now, so good luck and have fun building!
*poof!!! smoke&mirrors*
With kind regards,
Rashar.
