1. Do IVs, EVs, and Natures matter when offline?
Not that much. I have used Pokemon with terrible natures and IVs myself so don't worry about it.
2. Is it possible to transfer pokemon from 4th Gen to 5th Gen without Nintendo WFC?
To transfer from 4th to 5th Gen, you need two DS systems and have one with a 4th Gen game and another with a 5th Gen game and then you use DS Download Play to select the Pokemon you want to transfer, and then you need to catch them in the Poke Transfer Lab in the 5th Gen game.
3. How to transfer Gen 4/5 Pokemon to Gen 6? (Getting a 3DS soon woo)
You need to download Pokemon Bank onto your 3DS to transfer from 5th to 6th Gen. Read this guide on using Pokemon Bank's Poke Transporter feature:
http://www.serebii.net/xy/poketransporter.shtml