Without mods, party members don't get shrine quest bonus stats (I'm not sure if they get any quest xp). You have a maximum of 6 (8 with a mod) party members, including the Avatar. Classes don't seem to have restricted armor or weapons. Every caster get the same mana (int+ level).
There are skills that need to be purchased once for 150gp x current character level you only need to do this once for each skill so it is best to do it at the earliest available time. A
weapon damage forum post says archery can makes you slightly better with a ranged weapon (biggest difference is on the magic bow which may get 11.6% extra crap dps which is way less than the +1 ranged damage a level that the Avatar gets) and rapid strike makes you do less dps. Battle focus gives a huge boost and death blow gives a lesser, but still large boost. Parrying can more than double the armor bonus of your shield. If impedance works for the whole party, then it is a great skill that is diminished quite a bit by the crown which negates magic (can be gotten as soon as you can afford a ship).
The following only has "level unknown" for skills which I don't know what level they are gained. The manual may be wrong so they might not get some of them at all.
Classes:
Avatar
Virtue: Whatever you choose
+1 melee damage a level
+1 ranged damage a level
Spell Casting: Full
Skills: same as the class that matches the virtue you chose in the beginning
The Avatar is overpowered as usual. It is recommended to have the Avatar be a fighter or ranger for the skills, because they get full casting no matter what class you choose. Fighter is better at the start. ranger is gets its last skill 1 level earlier.Paladin has to wait until 5th level for battle focus.
Bard - Gwenno, Iolo, Toshi (has ring of protection)
Virtue: Compassion
Spell Casting: 1/2 level rounded down
Skills: archery, rapid strike (level 3), jimmying (5th level), traps (8th level)
This class is not very good. As an archer, they will do slightly more damage than other classes if you train the archery skill, but that is in no way worth the huge loss in melee damage. (The +1 ranged damage the Avatar gets trumps it and that is still low) If you want to have spell casting, get a mage or druid. If you want a melee guy, use Shamino, Dupree, and fighters. If you want traps and jimmying, get Julia. If just want jimmying, it comes late for the bard so you will likely miss a few chests, but you will start off with slightly better archery than Julia.
Druid - Janna
Virtue: Justice
Spell Casting: full
Skills: protection, impedance (level 3), channeling (level unknown), duration (level unknown)
fighter - Geoffrey, Gorn?, Maxwell, Sentri?
Virtue: Valor
+ 1 melee damage a level
Spell Casting: none
Skills: battle focus, death blow (2nd level), parry (5th level), recovery (8th level)
Mage - Mariah, Johne
Virtue: Honesty
Spell Casting: full
Skills: destruction, duration, channeling (5th level), impedance (7th level)
paladin - Dupre
Virtue: Honor
+ 1/2 melee damage a level
Spell Casting: 1/2 level rounded up + 1 but cannot cast offensive spells
Skills: parrying, recovery, battle focus (5th level), death blow (7th level)
ranger - Shamino
Virtue: Spirituality
+ 1/2 melee damage a level
Spell Casting: 1/2 level rounded down
Skills: parry, battle focus (3nd level), recovery (5th level), death blow (7th level), archery (never gets it despite being listed)
tinker - Julia
Virtue: Sacrifice
Spell Casting: 1/2 level rounded down
Skills: jimmying, traps, rapid strike (6th level), archery (level unknown)
This class is mainly only useful if you want jimmying and traps. See the bard section.
shepherd - Katrina (has swamp boots)
Virtue: Humility
+ 1 melee damage a level
Spell Casting: none
Skills: recovery, parrying (level unknown), battle focus (level unknown), death blow (level unknown)
This is basically a fighter that gets delayed access to their best skills (if they even get them).
A good party should probably include
Avatar with one of the virtues associated with a fighter class (gets full casting no matter what class)
Julia for locks and traps way before bards get them. I'm not sure if you miss anything good that cannot be bought. You could drop a party member and come back but that is tedious. The fights aren't hard enough to need all party members optimized.
Shamino and Dupre because they are partial caster and negligibly less effective at melee than fighters (once they have battle focus and death blow)
The rest could be all fighters because of their great melee ability.
maybe a mage or druid for the long lasting quicken and higher level spells (the Avatar can do this as needed but he doesn't regain mana as fast or increase the effectiveness of buffs)