OOC Discussions
Regarding the mage vs. warrior question, I think 1 warrior, 2 rogues, and 2 wizards will work as a party. 2 warriors, 2 rogues, and 1 wizard will do well, too.
Regarding the spirit warrior, yes, that can cause problems for the party as a whole. I won't disallow it, as it won't be any more trouble than you could already get into by having an apostate with you, but, it could exponentially increase your chances of detection by someone who might care.
Onto Fost's questions.
1. Looking at the Armor Training talent text on p.58, it explicitly states that the penalty applies to "all Dexterity-based tests and calculations (including Speed)." While the Armor Penalty entry description on p.76 only states that Dexterity is penalized if you aren't trained in the use of your armor, it doesn't contradict the p.58 entry.
So, yes, you give up Defense to get a reduction in damage. (Heavy mail, though, provides 2 extra AR vs. -1 penalty over light mail, and heavy plate does the same over light plate.)
2. No, a shield isn't a weapon, especially given that there's a separate Weapon & Shield Style talent.
Goals
Yes, please develop your character's Goals, as per p.44. Three are sufficient.