I would recommend you stay offsite, since you only want to do one Disney park. Offsite is much cheaper. Problem is, there are tons of options--it's esy to get overwhelmed!
We stay at Windsor Hills and love it--it's very close to Disney. There ARE developments that are closer to Seaworld and the Universal parks--sorry, I'm not familiar with them. I can tell you that WH has condos (in large "towers"), townhouses (attached in a row, most with private pools), and then actual homes. We rent a $BR, 4BA home for the 6 of us for ~$1200 for a week. There ARE cheaper options in WH, and certainly at other resorts and developments. We like WH due to its proximity to WDW and also it has a resort-like feel--a large community pool, playground, game room, movie theater, etc. We also like the specific house, which is why we're willing to spend a little more for it. Obviously, you have to choose what fits your family best, just letting you know the reasoning we use.
With 7-8 people, your best bet is likely a 3BR condo or townhouse. I'm not sure a
travel agent can be much help--they tend to sell resort rooms, rather than development rentals. I like vrbo.com, but there's also floridasunvacationhomes.com, mousepadsorlando.com and a host of other sites you can try.
A number of people on the Orlando board swear by Bonnet Creek--again, you might find cheaper, further from Disney. Most timeshare places in the Orlando area also rent out units.
BTW, Gatorland is still open--they rebuilt after the fire. It's a fun, half-day attraction.