A brief note before we start: including a homunculus in a party may be problematic (even for something from this thread). This is because as long as they know the location of their creator (probably at least 7th-level), they have to stay within 1500 feet of them, and having their creator die slays them as well. I recommend having them get petrified and Rock to Mud'ed in your backstory.
On to the actual monster. Homunculi have two construct HD, which means getting a ton of immunities at a minimal cost (though being tiny means no bonus HP, boo). They suffer penalties to charisma and strength, have good wisdom and dexterity, and obviously lack a constitution score. Land speed is on the lower side, but a 50 ft. flight speed makes up for a lot of that.
Homunculi also have a bite attack that deals some damage and injects a poison capable of causing unconsciousness. Not bad, but with the DC being constitution-based it's not going to get very high.
As a final note: homunculi explicitly cannot speak, which may influence some character concepts.
Personally, I think a LA of +0 is fine here, though I'm obviously interested in the forum's opinion.