First use brass fittings. For your valve question re to size, no it does not matter where you reduce. Remember the line to your grill is only 3/8" anyway. Yes Teflon for gas pipes is fine, or the proper plumber's "putty" either way be sure it's rated for gas use and never use galvanized steel for gas.
Please help! So I've got all of the connectors, etc. hooked up and leak checked no problem. When I connect the hose from the bbq to the quick-disconnect (male to socket), there is gas leaking from that connection. I would have assumed that once the hose is plugged in and locked to the quick-disconnect there shouldn't be any leakage of gas.
I believe the issue is that the connection is not tight enough and thus my question is, should it be? If this is the issue, are these faulty parts? Should there have been some type of washer to seal the connection? I can't imagine I'm the only one that this has happened to (I hope).
Any advice is greatly appreciated! I have this beautiful bbq that I can't use yet