Look out for overpriced box store bikes. An older, gently treated mountain bike makes for a good 'allrounder' ride, strong 26" wheels, 18-27 speed, the ability to put racks on for your commuting, (unless you like backpacks). You can gain road speed by changing to narrower tires, stay dry by adding fenders. Stay away from suspension till you decide on Downhill riding, bike paths and commuting don't really need it. Much as this sounds like abuse of LBS, try a few $$$ bikes out till you get a rough idea of the size you need. Not much causes more agony and abandoned bikes than one that does not fit you.