I like new stuff. But there are some advantages to buying something that's one to three years old, if you don't mind doing so. You escape the worst of the depreciation (saving thousands) and all of the out-gassing from the interior (that stuff can sting your eyes!). The little glitches (and maybe there was a big glitch or two) have been fixed under warranty. The disadvantages: you don't get to order something custom, there's no warranty period, and you sleep in a bed that's been slept in by others.
One of the problems we RVers have is called "two-foot-itis". We're often deciding that the TT we own is too big, or too small, or not as nice as another one we've seen. Buying the first TT used can avoid some of the financial hit. You find out while camping what you like and don't like about your TT, and when you decide what you really should have bought, you are only going to lose a little bit when you sell the current unit.
For the 4.6L, I'd suggest buying a TT with a smaller than average frontal area. Like, 7' or 7.5' wide rather than 8'. And maybe 100"-105" tall (not counting AC). It will tow easier, because frontal area (wind resistance) counts more than weight on the typical highway, at highway speed.
A lot of folks get carried away and buy a much bigger trailer than they need or feel comfortable towing. I started with a 23' TT with slide, then downsized to 16'-17' trailers, and have been happy with the smaller units. The small trailers fit into more campsites, too... which can be important if you want to stay at some tight NF CG.
