On the NEF question, there's a H&R/NEF forum right here on GBO that's as good as any I've run across on the net.
As far as making the proper sounds, I went through the same thing when I started trying to call predators. It took me almost two years before I ever actually called one in. You don't want to waste all the time I did trying to guess at what you need to sound like. I even had a little bit of experience from hearing a few actual rabbits squeal in my life.
Do what I did. Go buy(or order) a Johnny Stewart cottontail distress tape, and listen, no, "study" the sounds you're hearing, untill you get a feel for it. Once you've listened to the tape a couple dozen times, start trying to make similar(you'll never be an exact copy) sounds, and sequences with your mouth calls.
Once you've got pretty decent with the fixed reed calls, order you a Sceery AP-6, and practice with it a lot. By a lot, I mean if the whole family isn't mad at you, and every cat or dog around doesn't hate you, you're not practicing enough. Do your practicing at home, and "never" where you plan to hunt.
Most guys won't tell you this, but I will. If you're planning on ever getting truly decent at calling predators, you've got a Loooooong road ahead of you. The best part is, it's one of the best experiences you'll ever have the privilege of enjoying when it comes to hunting. Half the fun for me has been learning so much over such a long time by making silly mistakes, and seeing how even a juvenile predator can capitalize on it, and make you feel like a complete fool at times!
Have fun in your new venture, and good luck!