I stay offsite always. The answer to your question depends a great deal on how you usually deal with the parks. Personally, the last time I went was only for three days, so I planned what park(s) (park hopper) I was going to visit and on what days and then made my FP+ selections. I also had two places that I made ADR's for and those were mostly just to fit in with what I was thinking about doing.
Again, it is a personal thing. If you have a car, it is just as easy and no more time consuming to just go back to your car and drive offsite and eat most of your meals. For me I have breakfast before I go to the parks, usually have a quick service lunch and leave late afternoon to rest and have dinner offsite. I then return for the evening. I always have felt, in all my trips, that the little break rejuvenated me for the evening. Since I am not a parade or fireworks fan, I use that time to go on rides that are usually hard to get on, (like 7DMT) while everyone else is fighting for space to watch the other stuff. It just works for me. So, to make a long story longer, I only plan, location, FP's and whatever ADR's I might need... usually none.
A couple of years ago I didn't even make FP+ choices until I got to the park that morning. It was in the slower season and you didn't say when you planned on going. If it's the real busy season, waiting would probably a very disappointing way to do it.