For mild off road use and an inexperienced driver (no offense) a limited slip would probably be a better choice IMO. When you do get your truck, get good at wheeling it in stock form with open diffs, and you will be that much better driver for it. The Tacoma is pretty darn capable truck right from the factory. Find out what kind of wheeling you like to do and then start making upgrades. Every teenager I've ever known that had their dream car right from the get go (including myself) either totalled it or got themselves into ticket trouble within the first 18 months. Keep in mind, you will probably not be able to afford much more than gas if you plan on staying in school. Unless you are super fortunate at 16 and can afford two cars, you want to keep the one you have in as good as shape as possible, and aftermarket modifications increase chances of breakage. Sorry to sound like a dad(especially since I'm not one), but I too had stars in my eyes about what kind of truck I was going to have when I got my license, and within a month it was parked at the salvage yard cause I didn't pay attention to good advice.
I would stick to the limited slip. Better to learn how to use the truck, instead of just rely on a " miracle" device. Trucks still get stuck with lockers. NO, not as much. But, when you do dig in with a locker, it usually means a LOT more work to get you unstuck. Plus, the benefits of a LSD are always available. You would need to engage the locker, and sometimes, like with a wet, slimy road, it will be too late. Good luck, have some fun.
I don't think so.... it may be an option, but I believe the deal is the trd kit with the locker from Toyota. But, trd4u or something like that are sponsors on this board, and they have an awesome deal on LSD.... eaton . Look 'em up in the sponsors section. They are Texas based.