kbaby, the research does seem to indicate that early introduction of non-bm proteins is associated with higher risk of allergies. The best explanation of this association that I've come across is on the site kellymom .
Having said that, I weaned my older two at four months, as that was the advice at the time. Dd1 didn't really take to baby rice, and it was all a bit of a faffy waste of time. With ds I started off with banana, and he adored it from the first mouthful, and snarfed the lot. I was very tired from the bfeeding with him, and believe that he did need the solids.
With dd2 I followed current advice and waited till 6 months. Even at six months she had a powerful tongue thrust, and it took a long time to get her eating significant quantities. With regard to allergies, I haven't noticed a difference between them, but then again, we're not an allergy-prone family.
Early weaning won't necessarily help a baby sleep through the night, nor affect frequency of bfeeding, as the amounts they take in the early days is so small. There are scientific reasons for delaying weaning, as the site above explains, so if you can wait, I probably would. But if you feel strongly that you want to go ahead, then try it for a few days, see what happens and don't worry unduly.