I'm not spenidng all 2.5 weeks at Disney World (I wouldn't bother buying lightning lane for that.Just to be clear about the LL Premier Pass--the pass is for one park for one day only. And you get to ride each ride only once. I'm mentioning this because only someone with truly unlimited funds would be purchasing LLPP for every day of a 2.5-week trip. And if you do have unlimited funds, consider doing a VIP tour or two instead.
OP, since you're going for 2.5 weeks, you'll do fine getting regular old LLMPs and LLSPs. The Disney site lists what's available at each park.
I agree with a PP--YouTube videos are helpful.
My trip in total is 2 1/2 weeks. 5 days at Disney World, 5 days at Universal Orlando and then a DIsney Cruise!
We just booked the DIsney Cruise (that's the only thing open for purchase in 2026 right now)