I'll start with the nutes: I cant say enough of Technaflora's Recipe for Success. They have a $30 intro kit that will get you through a harvest and you decide. It's all 100% DWC compatible. A lot of people like the Advanced lineup. It's good too but much more complex to manage, expensive and the bacteria products are not DWC compatible.

The air stone is important, but the pump is even more. Get the biggest pump you can afford.

I disagree about the EC pen. But the pH one is critical. Follow the nutrient manufacturer's recipe and you'll be good. But pH may fluctuate daily or so, and if it gets out of check your plants will suffer.