Keidra,
the installation on computers two through four will be the same as the procedure used on the 1st computer. You just install DMPE 2 and activate it.
An iPad isn't a computer, even though Apple would have you think otherwise. The usual rules are not going to work. All you can do is use Siri or the local version of NaturallySpeaking on your iPad but it?s definitely not like dictating with Dragon Medical and not recommended. In fact, I don?t really recommend an iPad for anything but consumer use and I have 2 of them myself. If you?re serious about using a tablet computer, you should actually purchase a tablet computer with the Windows 8 operating system like the Microsoft Surface Pro 2/3 but note that I?m only using that as an example. The Apple iPad doesn?t have the proper operating system, amount of hard drive space or RAM.
You can use any analog microphone
http://www.knowbrainer.com/NewStore/pc/viewCategories.asp?idCategory=82 with a iPad/iPhone Adapter ~
http://www.knowbrainer.com/NewStore/pc/viewPrd.asp?idproduct=423&idcategory=36 on an iPad but again, you?re not actually using NaturallySpeaking or working with an actual computer.