If you’re going to adopt a false identity, I think it should have the same first name as your own. First of all, no one would believe that Scott Johnson is really just Scott Reynen's false identity. We expect more of our conspirators. Also, if you should ever happen to get your real and false identities confused, it would be much less noticeable and much easier to explain if your first name was the same. "What’s this letter to … 'Scott'?" Why, it's just a letter to me. Nothing at all suspicious about that!
I realize this flies in the face of conventional wisdom on false identity name choice. I recently heard someone (I can’t remember who) say that the only funny line ever on the Family Guy was Peter Griffin trying to pretend he was someone else and when someone asked him what his name was, he said "Pe...ter.......Grif....fin..." That’s a terrible false identity, of course, but I’m suggesting that it’s only terrible because it isn’t false. After meeting the falsity requirement of false identities, I think the goal should be to keep it simple, and the best way to keep it simple is to keep the same first name.
The exception to this rule is unusual names like "Icarus." If your real first name is Icarus, your false first name should definitely not be Icarus. This is my advice to people adopting false identities. I wish you best of luck in your life of lies.