I didn't read all of it, since I've apparently have alot of threads to catch up from last week...;
You can use the plastic check valves, overtime though, they'll get brittle and break. It takes quite a while though, so no worries. Some regulators come with check valves already installed. Orlando can help you there, he's an awesome fellow to deal with. He also has CO2 proof tubing. I'm currently using some of that black 'stealth' tubing from petco, though.
for a diffusor, what I use is an Elite Mini filter, it's ridiculously effective.