Kris, it seems to me when I was looking at buying an FJ new, it had a tow capacity of 5000#s and a tongue weight
capacity of 500#s. Really, if it's not in your manual, I would call the Toyota dealer service department nearest you just to check. If it is 500# tongue capacity, I doubt you'll need air shocks. Wanting air shocks is a different thing, they're great to have, but often not necessary.
With a tow capacity of 5000#s, I would expect Toyota made sure the vehicle was prepared to haul that kind of weight
, but again, it couldn't hurt calling the local dealer and asking. Keep in mind though that salespersons will generally tell you what you want to hear. You really need to talk to someone in service.
I would almost bet that vehicle has wiring under the dash for a 7 pin connector if it came with the tow package. That's the way my GMC was. The 4 wires I needed for the brake controller were taped to the top of my steering column, easy to do, but I already had the 7 pin plug factory installed in the back too.
I wish I could help more, but the bottom line is go to the source (Toyota) for specific answers to some of your questions. Good luck!