Hey Jimbo,I think you've already chosen a not-so-easy party-composition for ironman. It would have been easier if you had chosen a mage and a priest instead of the bishops, for they advance more quickly.
That said, a party of hybrid-characters would be more challenging than your current party, because they level slowly and you have to work on quite a few stats to make them efficient fighters, spellcasters etc.
Try something like Lord, Monk, Samurai, Ninja, Bishop, Bishop...
I think that a solo-game is the hardest way to play the game, because you
a) can't ressurect fallen party-members, for there's no one around to do so. He or she dies on his/her own, alone in the wilderness... I'd be really scared of those apuses around Marten's Bluff who can critically hit.
b) the character levels so fast, that even in the monastery you'll encounter tough opponents. It took my lone faery-ninja (yes, I know...) many tries to beat the pestilent rats, metallic slimes and poison seekers I encountered in the upper monastery. Not to mention Gregor...
Bye
Kuli