Hi there. This is the OP and I just wanted to answer a few questions that came up in this thread.
Here is the link to the BOG lunch FP+:
https://beourguestlunch.disney.go.com/ It is not yet letting me book for my dates the first week of May. My understanding is that there is not a set number of days prior to your desired date that you can book--you just have to keep checking to see when it opens up. It seems people usually post on the Restaurant board of this site when a new time block opens up.
I am not aware of any other "FP+" besides BOG lunch that is in addition to your 3 allotted FP+/day.
FP+ cannot currently be reserved ahead of time for guests staying offsite. Offsite guests must wait until they arrive at the park and make their FP+ using the kiosks. I think they can also do it with CMs carrying iPads for this purpose. To the person staying part offsite and part on, I believe you will have to wait until 60 days prior to your onsite ressie before you can book FP+. You will have to have your park tickets linked to your reservation on MDE. My understanding is that you will still have plenty of selections for times, so no worries.
I made the FP+ ressies from my desktop. I haven't tried it on my phone, but I just have to imagine it is easier to do on a desktop. To the person who asked, I think you will be just fine to wait and do it in the evening on the day your 60 day window opens--there is no need to do it in the wee morning hours.
Magic bands don't get shipped until, I believe, 30 days prior to your arrival onsite, so I made the FP+ ressies before receiving our MBs.
Not everyone would want to take my approach, but I admit I spent weeks planning out detailed touring plans for each park in anticipation of making my FP+ ressies, so I am going into it with a fair degree of confidence, which I think is wise, given another post I just saw about the glitches that can result from trying to change your FP+ using the mobile app while you are at WDW. Clearly, the system should be improved but, until it is, it seems careful planning is the best way to minimize the changes you will have to make, although surely unanticipated things may come up necessitating changes, unfortunately. I sure hope all my careful planning will pay off in May!