Realistically, if you limit your selection list to travel trailers or hybrids with a dry weight of less than 3500 lbs and dry hitch weight under 350 lbs, and overall length of no more than about 22' or 23', once loaded with liquids and gear your trailer should be quite manageable. The 4Runner might be able to handle a heavier or longer trailer than that, but why push it? Especially if this is your first trailer and you're just learning, no sense in going whole hog. Get something just big enough to house your family and go make some memories. ;)
BTW, I just bought a Lexus GX 470 earlier this month, and I took a 2800 mile trip towing an Aliner popup. Piece of cake!