I tow a 3,500 lb travel trailer with a 2016 4Runner. My setup results in a tongue weight of just over 400 pounds, and I use an Equalizer 4 point WDH. Loaded, my rig weighs about 4,200 pounds.
I previously towed the same trailer with a 2012 Tacoma which has the same engine but higher towing capacity (6,500 pounds) because the truck weighs less than the SUV.
My input:
1. You'll want more power at times, but the 4Runner will pull a trailer that meets the specs of the manufacturer, i.e. 5,000 pounds maximum.
2. The factory installed hitch is adequate for the job and will handle a WDH just fine.
(There is much speculation about hitches being "weak" and "bolted on", etc, but I discount this because:
A. I've looked at it. It's made with as heavy a gauge of metal as any aftermarket hitch I've ever seen;
B.The amount of weight being distributed from front to rear is on a magnitude of 250 pounds at the very most, assuming you max out the 500 pound rated maximum hitch weight of the 4Runner and assume that you need to shift half of that to the front (very unlikely);
C. The hitch is strong enough to support the lifting of the entire rear of the vehicle using a jack. This means that this so-called "weak" hitch is adequate to support at least 2,000 without deforming.)
D. Note that ALL aftermarket hitches are "bolted on".
3. The 4Runner is supplied with factory wiring and a harness for a brake controller. I use a Prodigy P3 with very good results.
4. I also installed a ScanGauge device that allows me to keep track of the temperature of the transmission fluid. If it ever gets really hot (not yet) I'll consider an aftermarket Trans oil cooler.
Your gas mileage will drop to about 10-12 MPG.
Good luck with your decision. For me, the 4Runner works fine. My trailer is a Winnebago Minnie 1801FB.
Greg