How viable would an all hard party be? I know there's only 1 copy of each instrument to be found, but that means spreading them around. One could work on buffs, another debuffs, while 2 deal damage and 2 heal with heal all and restoration. Would that be viable? Would it be helpful to import wizardry 7 instruments into wiz 8 for this?

Of note, there are 2 instruments that have 2 copies each: The Silent Lyre and the Dulcimer of Mending.

Healing will be a problem until someone reaches level 11.

If you want to do something like this, I recommend replacing at least one Bard with a Gadgeteer for variety. (I think that the Gadgeteer class is underused by most players.)

Of course, you could put a Bishop in the party for access to all spells, but that might dilute the experience of relying on a limited skillset to get through the game. (Any party can be made better with a Bishop, actually.)

Not very viable... imo a party of say six dragons or 6 elves is much more fun.

I guess it could work, because basically anything can work in principle, but there are some issues.

1. you don't have a lot of the important buffs (no Missile Shield, Enchanted Blade, Armorplate, no Element Shield, just to name the most important); Soul Shield you have to steal from Saxx (or recruit him).

2. you don't have wound healing until midgame and no conditon healing until late (so you need a lot of potions.)

3. for about the first third of the game some of your party members won't be doing a whole lot, since there are not enough instruments to give everybody something unique. This also means that at least half of your party will be quite slow in training their music skills.

This being said I think the idea is quite fun. As someone posted earlier, I would also incorporate 1-2 Gadgeteers, and maybe don't do a full 6-character party (4 sounds good). I would also think about changing two of the bards to Fighter and Rogue past level 18 to get a bit more variety. So I would try something like 2-3 Bards / 1-2 Gadgeteers (for a 4-player party) or 4 Bards + 2 Gadgeteers (changing 2 of the Bards to Fighter/Rogue later).