Several points have been covered but your limiting factor will most likely be the truck cargo capacity. If you add up the weight of your family and the things they cannot live without while camping. You will know how much cargo capacity you have left for tongue weight. Most trucks can pull far more than they can haul.
My 5000 lb. dry weight TT has a dry tongue weight of 406 lbs. But, loaded for the road my TT weighs 6200 lbs. and the tongue weight is 750 lbs. Dry weight mean very little. With my family and toys, I max out my F-150s cargo capacity.
Slide or no slide is a matter of opinion, I like them but they do add weight and cost. Also I would never own one that blocked access to bath or kitchen, other do not seem to mined.
Trailer values drop like a stone, never plan on high resale value, there are exception but not many.
Unless you are in a hurry, I always suggest you rent the size trailer you think you want and go for a week or so. You will learn a lot very quickly about the RV life style.
Good luck
