Even if it's technically illegal in many places, it is likely unenforced. I doubt police in most places would bother ticketing a cyclist on a sidewalk unless said cyclist was riding recklessly or stupidly. In situations where cars must move around a cyclist on a road, the motorists have control over how safe the situation is. On the sidewalk, the cyclist has control. Really, then, what is preferable to the cyclist? I'm not saying it's safer to ride on sidewalks all the time... if there is room for a bike on roads, roads are safer. But it frankly seems obtuse to suggest the opposite, that roads are always safer, no matter the specifics regarding how much room there is for bikes.

To the OP... you have a couple of months before you start commuting... why not go out during non peak hours on your off days and experiment with different routes. It shouldn't be hard to find one that you feel comfortable with.