typical newbie questions on a budget

I have 1998 Ford F-250 SuperCab that reads:

GVWR: 7200LB; FRONT GAWR: 3600LB; REAR GAWR: 4300LB

I'm really not sure how to calculate a safe towing capacity for it.

My budget for a trailer isn't more than $3500, and I've seen a number of options for older models on CL, but my lack of experience with various models has me guessing at the extent of repair/maintenance of what I'm looking at.

I have a great deal of construction experience and am not afraid of most repairs. It seems as though the thing to be concerned about is the amount of wood rot present, and that happens from bad roofs and seals ... among other things. I've done both fiberglass and aluminum work in the past, and I've read some people saying fiber is better, but can it be reused if you have rotten wood in a wall you need to replace?

I had also heard that the Holiday Ramblers had good construction quality, and I see a local deal on a 1984 35' Holiday Rambler Imperial (fiberglass body) travel trailer that weighs in at 7000LB dry. Even with stabilizer controls on the hitch, I'm not sure if maybe that isn't too much trailer for my truck. I live in Florida, without any hills, but I may need to put 250 miles per week on a travel trailer. I'd be happy with a 24' if the layout was good.

Thoughts and recommendations very welcome.

Thanks,
Steve & Ana
Florida