There are no bomb-proof harmonicas but a Suzuki Bluesmaster (a 10-hole diatonic) will survive better than most and is likely to work well out of the box (you can replace the reedplates too, cheaper than buying a new harp). I love my SP20s but they are definitely not quite as abuse-proof and they occasionally need a bit of tweaking to play properly. A Lee Oskar would also be OK. Cheaper than that and you're in danger of falling into the age-old entry-level trap, in which the instruments almost seem designed to put beginners off. As for key, C is quite high-pitched. G is a nice middling sort of key and he might even be able to play along with some jigs 'n' reels! As for tremolos, the planet is awash with useless cheapies, usually in the key of C. At the budget end they are likely to be out of tune and with inconsistent tremolo from note to note. The nicest ones are made by Tombo and Suzuki (in fact, generally I'd steer clear of any others). Hohner tremolos are usually tuned like a blues harp at the low end, so there are missing notes, and, in my experience, their quality is not quite as consistent as the two I mentioned. I wouldn't bother with a chromatic until he shows he getting quite good. Two more bits of advice: show him how to play gently, sort of huffing rather than blasting a jet of breath (the harmonica will last much longer). And beware of Ebay. Buying harps there is only for the suspicious and seasoned!