with gear stripping it can be caused by bashing in stupid areas with lots of stones or careless maintnenss of not locktighting engine mount screws but the thing i was thinking of is if you bout a engine say 1.5 HP it will have to much grunt for the alphas gearbox.
But as long as you maintain, drive on smooth surfaces and don't do anything to stupid with it nothing should happen.
And no doing doughnuts wont strip you gears but will strip your rear diff. But alpha 3s are mostly nitro toys not high performance tourers so just have fun with it.
Are you planning to get into racing?
if so i would get a new car as alpha 3s don't handle race situations and are very fragile.
I would suggest a RTR (ready to run) which comes with everything you need except battries.And go on from there.