Which RV choose

Thanks for your replys, I would try to answer to your questions.

I also think a 24" will be enough for us and a familly with 4 people if I rent it, but with a bed in the rear and a table.
There is not a lot of vehicule like that, so many 31" but no 24" with bed.
Yes I look very well the floor plan and I know the bath room is important.
What do you mean by lower miles on odometer on a V10 Triton Ford for exemple, 50000, 80000, 100000...miles?

I would like to keep this future RV as longer as possible, will try to use it for me once a year, about 6000 miles and camp in the Rv along the way, and maybe rent it.
I saw many Rvs sold in my budget with new tires.

What do you thing about buy a Rv in rental agency?
Is it better to buy it at a dealer or private seller?
Is the jacks are very helpfull?
Is the miles/gallons very different with a 25" or 31" ?
If later I would like towing a car behind, could I do that with a 25", the Ford V10 Triton will be better for it?
What do you thing about old Rvs about years 2000 with low miles, is it suspect?

I'm looking somethings like that and smaller

http://fortmyers.craigslist.org/lee/rvd/4816008347.html

http://fortmyers.craigslist.org/lee/rvs/4766800822.html

http://tampa.craigslist.org/hil/rvs/4832655078.html