As far as Disney is concerned, thee is no such thing as a split stay. It is simply 2 back to back reservations, so you book it as 2 stays.
As said above, if you book 2 room-only stays, with tickets separately, you will be able to book FPs for the whole time at 60 days from check-in day 1.
If you book the first night as a room-only, followed by a package with tickets attached, then the tickets are only valid during stay 2. At 60 days out from your swap-over day, you will be able to book FPs for the second stay.
Once you arrive, you can go to GS and have them activate the tickets early and use them on day 1. But you will only be able to book FPs on them once you do that.
ADRs are not "linked". So at 180 days from first check-in you. Can make them for days1 and 2. Then at 180 days from day 2, you can make them for the rest of your trip.
To get luggage moved, either call Bell Services and ask them to come and collect it from your room or take it down to them. They will move it for you but not guaranteed before late afternoon. When you get to second room, call and have them bring it up. No charge except tips at both resorts.
You will be homeless for a while. You can check in any time, but the room may not be ready. Pack a day bag if you think you'll want to swim, plus any medications etc. Or just head to the parks for the day and go back to the second resort when you're ready.