Lighting Hanukkah candles

I saw in the Gemara that there is an obligation to recite a blessing upon seeing the Chanukah candles, “who performed miracles.”
In a halachic ruling, the Rambam interprets that anyone who sees should recite the blessing on miracles if he has not already done so. The Shulchan writes that he should recite the blessing on seeing only if he does not intend to light a candle himself in the future, and the Mishnah Berura comments that the reason for this is that he can then recite the blessing on lighting a candle along with the blessing on miracles.
1. What is the root of the dispute between Maimonides and the Shulchan Arbiter?
2. Is the blessing “lighting a candle” dependent on the blessing “on miracles”? Then if I blessed on miracles, I cannot later bless lighting a candle.
3. The Gemara explained that one must recite a blessing for every sight one sees “about miracles.” Why wasn’t this interpreted?