Welcome to the forum.
1. .25/.50 should be fine, but if your bankroll drops too far, you can move down to .10/.20. Having played in both of those games, there is very little difference in skill level.
2. I would start will Full Ring. I would only move to 6-max once: 1) your bankroll grows higher 2) you feel very comfortable and "in your element" playing Full Ring.
3. Try the books mentioned so far (Tenner/SuperSystem II). I would hold on on the Ray Zee book until you are a bit more advanced. Read through as many posts as you can in the archive. I am a beginner such as yourself, so reading through some of the hands I posted may be helpful to you. Just search for threads posted by my screenname.
Here is a link for articles on O8 in cardplayer magazine:
http://www.cardplayer.com/magazine/category/omaha_8b
Also check out
www.o8poker.com and Annie Duke's articles on 08 here:
http://ultimatebet.com/poker-strategy
Read through as many posts by Buzz as you can. He's very knowledgeable about the game and explains things in such a way to make them easy to understand for a new player.
He also has written for the 2+2 Internet Magazine. You can private message him, and I'm sure he'd be willing to send you any old articles.
bbartlog is another poster who has been very helpful. His expertise is more in the realm of pot-limit, but he provides useful insights nonetheless.
There are a number of other very successful posters as well. Sometimes you have to wade through some unproductive trash talking and other low-content stuff, but other times you will find some constructive posts. In general, they are willing to help provided you put spend the time to put thought into your posts.
Hope this post helps you in some way.