you can schedule fp+ 60 days out, if you have tickets linked in the app. The fp+ option will become available once you link the tickets. You pick your park, then your 3 attractions and you get options a,b,c, &d to pick from which have all different times and order. You can then change your times to get different times or order of attractions. I think there is a block out window around adrs from what i read on these boards, i didn't actually make any.
If you plan on park hopping, i would make my reservations at my 2nd or 3rd park for the day and use rope drop it the am. I would fp, tsmm as soon as you know your dhs day, if you want a prime day slot. I booked it for 2 days, about 20 days early and got 12 and 1pm. (i booked my dhs fast passes for morning/afternoon, even though we park hop sine we always start at dhs and don't go late. Ds3 favorite ride ended up being tsmm, so i tried to add a 3rd day there and they were not available at all; app said stand by only.)
dhs and epcot are difficult because of the tie ring. I booked soarin', ds3 ended up being intimidated by the loud noise that is tt, so older ds and i used single rider line. You will see crazy things with fp+ usage. We waited sb for disney junior on stage and saw people scanning their fp+ bands for entry with no stand by line. I was not successful in changing my fp+ ressies on the fly(maybe our android is too old?). Tbh, i didn't use any fp+ at all the day we met our florida friends at ak, we just waited in safari line and we let multiple expire because we weren't able to get to our times. For example, dh and ds13 left tsi at 2:15 for a ride on the haunted mansion standby(posted 20 minutes) and we had 3:20-4:20 fp+ at buzz. They finally made it to tomorrowland at 4:35 due to line not being 20 minutes, but closer to 60 then, ride shut down multiple times. Ds3and i almost missed because tta took us almost 35 minutes to make our round trip. We ended up trying (and was no problem) or bands about 4:30. We couldn't reschedule the 2 we didn't use. Epcot is tough because of soarin, tt, and maelstrom all being tier 1, choose 1: So what to pick and use for other 2 captain eo and figment? Just annoyed us, because you want those other 2 later at mk when pp is 70 minutes, kwim?
Happy planning and have a great trip!