Way to early to even think about decreasing bottles. Formula is still his primary source of nutrition. Solids should always be fed after the bottle (maybe an hour later if you prefer). I skipped cereal altogether and went straight for fruit/ veggies. Started with carrots, squash, pears, apples and just kept going one at a time. Don't let his allergies discourage you. The MSPI may just be a one off.
Good luck, mama!