1a. A mod (short for Modification I believe) is a collection of data files that modify your game, adding either story content, items or NPCs or a misture of all or some of those.
1b. Each mod should come with instruction on how to install and impliment them and an outline of what the mod does, if a mod comes without a readme tht does that, it's not trustworthy anyway so bin it.
1c. There are risks in downloading anything from the web, viruses attach to anything executable, and that includes most mods. But just visiting any site can trigger unwanted spyware, so wear belt and braces. In other words make sure your virus protection, spyware protection, and if you have it, firewall are up to date.
2. No, the level limits are the same for both games on both platforms, but, it is possible to get round them with the PC version if you're prepared to use an editor.
3. Not as far as I know, but I don't own one (wouldn't want one if you payed me) so (shock, horror) I could be wrong, it happens once a century or so.
