We go to Florida most years (not always Orlando though - not going this year). We start looking at flight prices as soon as they're released (about 11 months before travel dates), and for the last few years have found BA flight + car hire to be very competitive, plus they're direct (although we've flown indirect many times too). Depending on if you only want to stay in Orlando, you could also look at pricing for Miami (about a 4-5 hr drive to Orlando) and Tampa (1.5 hrs drive).
We always stay in villas as I like having our own pool, the quality in Orlando is generally very good. We stayed near Champions Gate last year, but have also stayed at Windsor Hills many times, it's a great location for Disney. The Universal hotel trick for fast passes is great, although for so many of you, could prove very costly.
For villas, I generally start looking on HomeAway (which is the same company as VRBO, OwnersDirect, HolidayRentals etc), but you could also look at AirBNB. I've never used AirBNB, it always makes me a bit nervous, but I've never had any problems with HomeAway, and use them generally twice a year in US and European holidays. There will be thousands of villas, so make sure you filter down (so tick box for private pool, minimum bedrooms, air con etc etc).
I've done Orlando with extended family, and my main tip is don't try to do everything together (this of course may not be practical in your circumstances). Sometimes it's just easier to work out who wants to do what (ahead of time), then split up and meet up at various points for lunch, drinks, parades or whatever.
Good luck with planning, you'll have an amazing time!