I don't know the answer to the first question, sorry.
I believe I can answer the other two. Here goes:
The general rule is, if you don't specifically target certain letters for certain schools, LSAC will send your letters in the order by which they were processed. Meaning, if a school only requires one letter (and only accepts one), the letter that was first processed will get sent to that school.
The answer to question 3 is that LSAC will send as many letters as the school allows for. Even if a school requires only one letter, they may accept up to three. In that case, all your letters would get sent. If they require one, but accept up to two, your two first processed letters would get sent and the third would not get sent.
Hope this helps.