Nice truck. You have not stated at all how you intend to use this truck, that would help alot and till then you will get answers all across the board or none at all. Since you said it is your tow rig, i will assume you use this only on the highways or very mild washboard roads.
Sounds like your dialed already in the rear. My thoughts- Alcans are great springs and they will build you what you ask for. Springs built for a 700# load will handle purdy rough without anything in the bed, so plan on carrying something all the time. Lighter spring rate and adjustable airbags might serve you better if you spend much time in it without that load. Other than that, you must need a set of rear shocks to dampen the ride. Choose your flavor, they all will do their job. I like Fox, Radflo, or Icon but all will work.
Front- you may want to level the front out to match the rear. On a tow rig this could be done with something as simple as coilover spacers- cheap and factory ride retained. However, since youve said the suspension may be shot and already stiffened up the rear quite a bit you may want to match the ride quality as well or it will have a strange buck in the rear. Again, quality coilovers are abound and you dont need the top of the line to tow highways with. 2.5" lift coils will not affect your geometry greatly so a simple coilover/spring unit swap and alignment will work great. OME, Bilstein, any others will work. Stock rims should handle that lift w/o A-arm rubbing or could get some small spacers to alleviate it if they do.
Check out
www.wheelersoffroad.com for lots of toyota lift ideas. Also
www.tundrasolutions.com and
www.tundratalk.com have many threads on just this subject. Plenty of vendors here on Expo sell kits as well and should be able to give great advise.
give up some more info and people here will be able to better steer you.