I vote ditch the books. That's just my opinion, but here's what I feel happens.
1.) You start out reading these books with zero knowledge of poker strategy
and suddenly you find yourself trying to understand why three authors contradict theirselves or why an author uses a certain tactic in the first place when you really have no experience with that situation to begin with.
To be quite honest, I find the best way to learn (once you understand the basic rules) is to simply start playing some low stakes games - be forewarned No Limit, Fixed Limit, and Pot Limit games all play differently in how people strategize. You might think it's going to cost more money than you'd like, but the truth is that if you play smart bankroll management and just play a very tight game, there's no reason you'll go rushing through it and often it'll cost less than buying books, DVDs, or signing up for professional training. Even $25 deposit at penny stakes is going to help you a lot.
2.) Like I said, I think jump in right away, once you understand the rules. But don't go playing mid stakes until you grasp the concepts of low stakes. Sometimes higher stakes games allow you to do certain tactics, simply because people are more aware of their financial risks whereas at low stakes people might be a bit more liberal with their calls and raises; however, at higher stakes you'll be with higher competition (most likely) and so even if you feel you've got a good run going, it's only a matter of time before the sharks attack.
3.) Sit N Gos are probably the best bang for the buck. Heads up games have some specific strategies that tend to work, but if you play in Sit and Gos enough, you'll eventually end up heads up and slowly learn those concepts. Cash games might seem like a good way to learn, but you can usually get far more poker and far better odds
of winning some decent cash in a Sit and Gos. For instance, at No Limit low limit ring games (cash games) you can easily find yourself facing calling a $1 or $2 even at $.02/.04 tables, and that can be gut wrenching calls when you know little amounts add up if continually make the wrong call. Compare that to a single $1 in that lets you start with several chips and can play for quite a while.
4.) The number of players generally plays a part more in card odds. The more players there are, the more likely another player has 'X' card and the more people you have to bluff. Pots get larger and you have more rounds where you don't have to play the blinds. It might be easier to win at 6 person table, but I think you'll get more learning experience from a 9 ring table where you'll get more poker for your money to learn.
5.) The games play differently strategy wise, so while the rules might be the same (with the exceptions of bets), you'll probably find yourself developing a different play style for each, so it doesn't really matter. The obvious thing is that the amount you can win and therefore lose in fixed limit games are limited, which is nice on one degree because it's less likely you'll be put in a situation where you have to make a tough all-in call on a great hand only to have the opponent hit a gutshot or river draw.
6.) Omaha isn't hard to learn, you just have to watch yourself because it's often easy to overlook things or misread hands if you play a lot of time at holdem. You have to use two cards in your hand, which often causes a lot of confusion. At least two and only two.