Does it make a difference in range if the router is mounted higher than lower? I mean if I put it on the top shelf vs. on the floor, will I notice?
The only way I know that it would make a difference if there are more objects lower than higher that might interfere with reception etc. I just keep mine up high because i figure less chance of things getting in the way.
Its a radio signal so it is susceptible to all of the normal things that degrade signal quality such as, solid objects. I would suggest a central location with minimal walls or other objects between the router and the desination computer(s).
Yes and no. It all depends on the amount of information that you're sending out. If someone really wanted to access your home wifi, it would just take time, but if someone is out wardriving and they see your 'closed' WAP vs. your neighboors open WAP, who do you think they are going to fuck with. I would consider WEP a deterrent vs being security.
To actually answer your question, it really doesn't matter. Putting it up on a top shelf actually increases the distance between the AP and your computer in most cases. The only reason I would do this is if the computer was on the second floor or if that's just where I wanted it. We are only talking about a few inches different.