How possible would a no party, all acts, no major glitches run be in honour mode, strictly playing as Tav? I know it would probably be long, but is it even possible?

There have been solo honour mode challenge runs runs, so it's possible. You'll have to figure out what to do for certain encounters to get through them. Ketheric and Orin would be rough but I think it should still be possible as a low level character.