Good questions and concerns...Tires are time-stamped carefully these days, there are actual date codes molded on the carcass, and older tires are a liability. Setting on the lot for two years could be 3-year-old tires, many say that six years is max life, so you may have some negotiating room here. Read the tire date codes, they should be quite visible on any tire built after 2007...I would at least shave something off the upgrade to 225s, and yes, I would step up for Load Range D.
Sounds like you're on the cusp for the 18-footer, and I am still swayed in that direction. You can readily "live" with the 16-footer, and putting the tool tote on the tongue is not a major issue. You can even get the battery inside the tool box on the tongue to protect and secure it. You may want a full size battery if you anticipate adding a winch for loading a "wounded" Jeep or another vehicle.
I checked out the hitch, and the idea of a friction sway control built into the hitch is nice. When Rick Preston outfitted me to the gills years ago, we went with a heavy-duty, Draw-Tite equalizing/load distribution assembly with torsion bars that enter the bottom of a massive ball mount. The mount weighs plenty, the bars are hefty, too. Rick added a "sway brake", which is actually a sliding friction brake that serves much like the hitch you have shared.
For my longer wheelbase Suburban 4x4s and the Dodge Ram 3500 4WD chassis, I really could not feel much difference with or without the use of the sway brake. If we were back to the Toyota FJ40 Land Cruiser's 90-inch wheelbase towing a 21' travel trailer across the Mojave Desert in a crosswind, I would definitely mount the sway control brake and use it! The brake has its own smaller mounting ball/studs and attaches readily with hitch pins.
I'm not minimizing the importance of resisting side sway. I'm simply sharing my own experience. When we trailered the XJ Cherokee to Moab at 70-plus mph across the wind-swept Bonneville Desert, we did just fine with the heavy duty equalizing/load distributing hitch and no add-on sway control brake...There is nothing wrong with a load distributing hitch assembly that has a built-in sway control, so if the price is right, get it! Given that you have a heavy camper on the truck, I would go with both the load distributing hitch and a sway control of some kind.
When selecting a load distributing/equalizing hitch assembly, look at its load rating. By design, any equalizing hitch will work if rated for your anticipated loads. If possible, get an equalizing hitch that is easier to install and remove. Ours is very bulky, but I don't mind a good workout!
As for your concern about a shorter trailer and the effectiveness of the load distributing hitch, by design the hitch levels the truck and trailer, regardless of the trailer's length, so there should be little difference in the handling with the 16- versus 18-foot trailer. The maneuverability would be slightly better with the 16-footer, the 18-footer would have more flexibility for loads and hauling different wheelbase vehicles. Handling physics would be slightly different but minimized if the trailer's axles are placed properly for a load like your Jeep Wrangler.
We haven't discussed wiring, lighting, the post jack and tie-down provisions, and these are important, too. Make sure the trailer you pick has reliable brakes, well routed wiring, good lights with common replacement lenses and strategically placed D-rings. Get good straps, and check out my tie-down article at the magazine for ideas on tie-down points, axle wrap straps, chain and ratchet straps. There's a lot to consider when trailering and hauling a vehicle safely.
Sounds like the bargains are disappearing fast. Pick the trailer that fills your needs, and if aluminum wheels are not expensive, they do eliminate rust issues. Galvanized steel is okay, but the galvanizing seldom lasts at the wheel nut seats—or when tires get dismounted and re-mounted, or wheel weights get installed and removed. Aluminum can oxidize, too, but the effect is less of an issue cosmetically. Aluminum can be lighter, too, but not much lighter at these wheel sizes.