Bah, it'll be fine, just get the car looked over COMPLETELY when you get it, don't skimp, fix what needs fixing and keep it maintained. Don't bother with modifying it for power, maybe do suspension and brake upgrades, maybe wheels and tires.
Enjoy it for what it is if you want it to be reliable for you. If you want something that will be fast, you're looking to spend money.
Decide what you want right now, if you want something reliable and fun, there are other cars too, if you want a Supra and want it to be reliable and fun, keep it maintained. If it is in good condition and you keep it up, it won't give you problems.
If right now, you are thinking about getting a Supra and that you can get more power out of it, that's all well and good, but if you aren't thinking you're going to need to spend maybe $1500 right out of the box for some maintenance work, you're fooling yourself.
Like I said, plan on spending $1500 the day after you get the car for maintenance, go over the vehicle, change rotors, wheel bearings, or whatever it needs, it may need more than $1500, who knows, but you need to be commited right from the get go to give the car what it needs to be reliable.
If you aren't willing to spend what it needs to get it up to par to be a reliable car, you're asking for trouble. So many MK3 owners spend money on subwoofers, speakers, wheels, boost controllers, turbo timers, when their power steering lines are leaking, they're drive belts are cracked and their driveshaft has a dead center bearing.
Don't skimp on maintenance, and the car will be great to you. I think it could be a great first car, provided you don't treat it like 90% of the other 17 year olds who buy them do.
'nuff said.
(PS: I voted "Yes").