We initially ordered a 19 in early 2014, and then were graciously allowed to switch that order to a 21 at the annual gathering in Osoyoos, which we attended in a mini-van before completing our build sheet. Switching sizes may be much more difficult, if not impossible now. I'd definitely visit both models and lie down in the beds of both, as we did. The somewhat narrower bed is my only concern, and has me thinking from time to time about the fifth wheel, now that we have a truck.
On the 4Runner issue, we towed our 21 for over 20,000 miles with a V-6 2003 4Runner, and let us say it was, uh, adequate.
I added a transmission fluid cooler and a Scangauge II to watch temps. With the newer V-8, you should be fine, except I do recommend extended mirrors. I can't really advise on sway control, since I bought a used Andersen hitch assemly with sway control which has been fine for us, although others have had complaints and ETI no longer sells them.
Again, I highly recommend that you try on both size Escapes before ordering.