There's not a lot of great KB advice on this forum, unfortunately.
Don't order from Onnit. There's no reason to do that, at all. Paying for shipping on a KB is a waste of money as well. Those demon bells look cool but again, you're paying for something you don't need. This is kettlebell work, not a fashion contest.
The T-Bar is amateur hour and you can't do one-handed movements with it. Don't waste your time. Adjustable ones are for girls in yoga pants. They aren't great and typically lack a thick handle, which isn't going to help your grip much or bulk up your forearms. No one who does serious KB work uses adjustable bells.
Go to play it again sports and buy a 16kg kettlebell. I prefer mine without a rubber bottom, but if you're working out at home, that can save your floors from scratches and what not. Doesn't make a big difference. They have new and sometimes used. Compare the handles and grab the fattest one you can. They come in different sizes, although it's not marked or labeled. Sports Authority has kettlebells but they're often in lbs and have a finish that chips easily. A finish that starts chipping on the handle will chew up your hand(s) in a bad way.
Most people do the swing incorrectly and think they look sweet doing it. Don't be that guy. Practice on your own and if there's an instructor in your area, shell out the dough for an hour of instruction. Find someone with certification. Tons of amateur kb "instructors" who do most things incorrectly/inefficiently. Refining the finite mechanics makes a BIG difference when you're dealing with more weight and/or volume. It'll also prevent injury. An instructor can also show you how to clean properly, which is important when you get into higher volume workouts with a lot of overhead work. You can figure all of this out on your own, but having a set of experienced eyes on you with a mind for mechanics is well worth the money spent.
Regarding workouts...I prefer Steve Cotter over Pavel, but it's all preference.
This DVD set is what has given me the best results. There are 20 minute workouts where your "rest" period is around the body passes and they get you
fucking shredded. The ab/core specific workout is ridiculous too. There are also workouts for size and strength, but require 2 bells. Pavel's stuff is great, but I prefer Cotter based on instruction, his background, and my results after making the switch to his workouts.
I would also
highly suggest avoiding the overhead squat until you're supremely efficient and flexible. You can seriously damage your body that way, even if you know what you're doing.
Good luck.