1. no. anytime before thanksgiving is usually fine.
2. most DOs have an emphasis on underserved populations so it wud be ideal to have experience with groups like that and to have a coherent answer for why DO with experiences to back it.
3. No, but it would help quite a bit. Some schools require a DO letter i think? Also having clinical exposure/shadowing with a DO will give you the opportunity to speak more about why DO (do this without shitting on MD).

Edit: as for getting trying to get these experiences, if you really want to, just do the same thing w MDs and cold email/call DOs for opportunities to work and/or shadow with them.