Quick release hubs allow the wheels to be quickly and easily removed from the frame, which makes a bike easier to put inside a car or storage area. Virtually all bikes made today use indexed shifting. If you're getting a mountain bike or hybrid, the bike will probably have 21 speeds. The few road bikes in this price range will have 14 or 21 speeds. Get whatever one you are comfortable with.
Most manufacturers offer both types of shifters in alternating models.
The more aluminum parts, the better. Again, aluminum is lighter and stronger than steel for most bicycle component uses. Look for aluminum cranks, brakes and levers, seatpost, handlebars, and hubs. Spend your money on a good, sensible bike. If you need to upgrade later, it's easy enough to do.