First congratulations on picking the trailer before the truck.
Ignore the names like Extreme, Ultra, etc. anything. 8000lbs dry weight is about average for a 30ft 5er. It is not light weight although it may be "lite" as in reduced calories ;)
Ask for the Gross Weight Rating (the most it can safely carry) of the trailer, pay no attention to the Dry weight.
Shop for a size and layout that you like. Look for convenience and ease of maintenance.
Get at least 16 inch wheels, I consider this an important feature for a 5er.
Tank Capacity, automatic levelers, hydraulic vs cable slides and landing gear, awnings, BBQ's, etc are all just options and there are lots of forum discussions you can search to get various opinions on.
If you are full timing I think a comfortable living room area is vital. I want two, good size comfortable chairs, which for me was an aftermarket purchase, but I still needed the space to put it in.