If you expand a bit on what you would like the build to be able to do, then people might chime in with more suggestions. Do you plan on lots of stealthing and decent sneak attack damage? Or casting bard spells and a strong bard song? Or mostly a melee toon with the other classes for extra skills and better saves? BTW, unless you are thinking in terms of a dexing character who may need Weapon Specialization to deliver decent damage, you should consider taking Champion of Torm in place of fighter.
As icywind1980 notes, there are some builds with that combination out there, though few will be elves, since that invites the possibility of a 40% multiclass XP penalty. Unless you are diligent in keeping at least 2 of these base classes within one level of one another, it's hard to recommend elf here. Of course, it's not hard to finish HotU with fewer levels, but bear in mind that there is also a penalty for each henchman, so that will be another significant factor, unless you plan to solo all or most of the module (which is also very doable, but it can be a challenge, depending on your play style). BTW, unless you are thinking in terms of a dexing character who may need Weapon Specialization to deliver decent damage, you may consider taking Champion of Torm in place of fighter.
As you know, HotU will take your toon to level 27 or 28 in a run where you do all the quests with no significant XP penalty and don't farm respawns. (That drops to possibly level 25 with a 20% XP penalty). That means that, unless two of the classes only get a level or two by then, this sort of character will be sort of a late bloomer in terms of getting class features that come at higher class levels.