Question #4: How much work is this mower going to do? Corded electric mowers generally cost the least but you have to walk with a cord behind you, which is pretty inconvenient. This could become quite a nuisance if you have to mow a large area. Battery-powered mowers have no cord but will only last for 20 minutes at a time. If your mower will get a lot of wear and tear, pick something that will hold up to it like a gas powered model. You want to make sure you're paying for quality and not bells and whistles. One way to ensure this is to look for a mower with a strong engine, which usually means a brand name. It should have all metal parts too, nothing plastic.
Ultimately, your budget will probably make most of the decisions for you but if you go a little cheaper now you might find yourself picking out a new one next year.