You can pick up a tank at most sporting goods stores too - a lot of them will do your first fill for free when you buy one, so it's not worth it to save a few dollars ordering online when you make up the difference the first time you fill it. I think I paid about $24 each for my 24oz tanks but the 18 and 20oz tanks were cheaper. It doesn't cost much more to fill a 24oz tank.
The aquatek mini comes with tubing (but it's not great) and a bubble counter/check valve. I'd recommend a better check valve, CO2 proof tubing, and a diffuser. I actually like the aquatek diffusers.. I've gotten very consisten fine bubble output with them, unlike some of the glass ones I've had.