For what its worth i tow my car hauler with my tacoma, from my house to my home town (500 miles) i go through the flint hills which are not mountains but have some long decent inclines. my trailer weighs 1900 lbs with no tools, and about 2100 with the tools in the box. With one of my old toyotas loaded (3200 ish lbs) spare tires (truck, trailer, play truck) and the normal assortment of gear ( jack, winch, chains, tensioners, cooler, 2x 5 gal fuel cans, 5 gal water, 2 cynder blocks and my ramps @ 65 lbs each) i average 12.6 mpg in my 2013 with the 6spd. I run a little tounge heavy because of the tool box (knack box welded on the front) is heavy. And i generaly tow in 5th gear 1:1 ratio. I have trailer brakes normally but they are currently broken, and 5 leaf spring pack in the back. The truck tows great and i could not be happier, accept i want my trailer brakes fixed!
the user that mentioned wind drag is right, it makes a big difference and here in kansas its windy as hell. the manual is so much nicer than the auto was.
In my 2012 auto i averaged about 10.5 mpg and the truck worked harder but i never had any issues with overheating or anything else. The one time i was in a hurry with a full load (75-80 mph) i got less than 10mpg and had no overheating but the truck did hunt for gears if i was in normal drive and not in 4th gear.
I have towed with 1st gen taco's extra cab, double cab and regular cab (3rz and 5vz no 2rz), 79-83 toyotas, 84-88 yota's, 89-95, with both 3.slow and 22re (i would rather the 22re) a 3.slow 4runner, 2000 landcruiser (6 mpg), 2004 dodge 2500 cummins auto, 86 ford f250 6.9 idi 4spd, 93 ford f350 7.3 auto, 2002 chevy 1500 v8 auto, 2000? f550 dumptruck 7.3 7speed, military vehicles and a 2004 tundra v8. and a 2007 tundra 5.7
one of my favorites is the tacoma for the same reasons, decent fuel economy and i love the truck and for the occasional towing it does great. The 2nd gen tacomas are way better and happier than any older toyota trucks (including that stupid 2004 tundra)
I would be comfortable towing a 5000lb 25 ft camper, i would expect 10-11 mpg and would want trailer brakes. and i wouldnt expect it to be fast but i would trust it to get me wherever i was headed and be safe doing it. The tacoma is lighter than a full size for being pushed around but the 2nd gen is no feather wieght either and has a lot more ass than a 89-95 toyota.
Best thing i can recommend is find one similar and give a tow and see how it feels to you
as for a distributing hitch i still have the factory hitch, havent tried one since im happy with what i have
trailer brake controller, well i cant tell you what i have because i have moved it from truck to truck for years and there are no stickers or markings on it. but any reputible brand of progressive controller would do just fine. and the 2nd gen taco even has the wires already ran for you.