For some reason I don't really like the chanter, but I'll have to try. I feel the +2 engagement on the fighter is useful to prevent enemies from going on my weaker backline, and his modal gives quite a good Deflection too. At higher levels, he gets aoe knockdown and other defense boosting abilities that make him hard to replace as main tank. Besides, if a chanter was my main tank, I'd have to lower his defensive stats a bit to raise INT I guess. I'm looking at his higher lvl invocations though right now, and I might just pick chanter instead of paladin as my 2nd tank (which already had 18 INT in my build). Being able to summon a drake (3rd level invocation) definitely sounds good.
For the secondary stats, I prioritize resolve over perception because of the bonus to concentration. Some mobs seem to go behind your tanks whatever you do, such as Specters if I remember the name well, so I figured concentration would help.
I'll have to think things over about the rest of your post. Going chanter instead of paladin would help with the dmg, but I'm having trouble setting stats for him. Will a lower Might on the chanter also lower the power of his buffs to allies or of his summons? I want him to be tanky, but if I want him powerful I'd need to compromize on his tankiness to improve his Might. Another problem is that the chanter got low endurance and health (according to what it says at char creation), while the paladin got high... How's that for a chanter? :
10
15
3
18
14
18
I don't mind his offensive spells doing less damage, I'd pick him more for his buffs and summons. Should I lower Con (since he gains lower hp/end per lvl up anyway) to raise Might? Maybe 15 might and 10 con?