Most of my trips are planned 3-4 months ahead, some as little as 2 months ahead. I occasionally have to plan a trip up to 9-11 months ahead if it's for a big, planned gathering or group event. I don't so any paper planning, computer or spreadsheet planning...I just think about when I might want to go, search for room availability, and book.
I'm flexible about where I stay - I'll take my home Boardwalk if I can get it, but when I'm booking 2-3 months out, I know I'm not likely to find much, so it often ends up being OKW or Saratoga, which is fine by me.
In a perfect world, I'd be able to 'plan' my Disney trip about 1-2 months out and get whatever resort I wanted, would not book any ADRs or advanced LL stuff, decide what restaurants I wanted to eat at that morning or afternoon, and call to grab a ressie. Make random decisions each morning which park I feel like hitting. That used to be how I did Disney trips for decades, until 15-20 years ago or so when they started putting more and more advanced planning options out there, which squeezed no-planners like me out of most restaurants, resorts, rides, etc. Now I participate only as much as I need to in order to hit a few of the resorts, rides, or restaurants I want to hit while I'm there - I still never buy Lightning Lanes, some nights don't book any ADRs, and never do online check-in.