Actually, quite sadly, The regulator shown won't fit a standard bottle. It needs a special fixing that the supplier sells separately at a premium. Go figure.
The Guy selling the paintball cylinder is reluctant to sell it for any purpose other than for a paintball gun. Apparently, some moron filled one with compressed air and it exploded. Go figure.
I bought a nicer looking diffuser. The wife wants me to test that out before I buy a full CO2 setup. (Her thoughts: If there is enough CO2 in the air, why add more? Try dissolving more of it instead of relying on an airstone or bubble tube)
Solenoid seems trustworthy, but without a CO2 tank and/or regulator, I saw little point in getting the solenoid.
Will update this post as I get more information.
So far it seems, if you're going to bother, go all out and pay for a decent setup. Saving little amounts may cost you big amounts.