First of all, do you know anything about coding? Sorry if I'm wrong, but I think you don't have any experience at all...
Also, lua ain't going to help much at all. You need to know C# (Or what ever HL2 was build on) references. You need to own Microsoft Visual Studio, which costs thousands of dollars. Lots of experience. Lots of custom models, unless you are going to use Day Of Defeat: Source models, which isn't really possible. Because it would be stealing.
Hiring coders is a bad idea. If you are the leader of the team, you are going to need to be the coder and usually the leader mapper. You need to build .fgd, so other mappers can make the objectives.
https://developer.valvesoftware.com/wiki/My_First_ModAnyway, good luck. I hope you will succeed. I have always wanted to try World War games on Source engine.