According to my opening book, it isn't a problem. I don't care for it myself, but then I wouldn't play Nc6. I don't think e5 is a threat: Nobody plays that because normally you have dxe and Nd7 and the pawn is attacked. There is not a huge difference between option 1 and 2, except of course for g6 and Bg7. You could run into an early d5 attacking the c6 knight, but you're used to that.
I can't help with your option 3.
I would not play the French with a knight on c6. It's blocking the c-pawn so you can't pressure white.
I think 5 and 6 are playable transpositions.
I wanted some opinions. I took about a 2 year break from the Nimzowitsch to learn some other openings. I want to play it again because I love the line 1.e4 Nc6 2.d4 e5 3.d5 Nce7...
The problem is I've never played e4 e5 games a day in my life. I'd rather something people don't see every day, a position I know better than my opponent. So after 1.e4 Nc6 2.Nf3, what would you do.
1. There's a line where you play d6, Bg4 and then e6 that I'm pretty sure Tony Miles played.
2. There's d6 and a pirc transposition. This is recommended in the book The Dark Knight System and I have the book, I just struggle learning from chess books. Anyway, there's a funny line where white plays an early d5 and the knight goes back to g8. I've done well in those lines. The most critical appears to be white playing e5 before you get a chance to.
3. The Colorado Gambit, 2.f5. It's not entirely sound. I'm playing at the 1300 level and do ok with it, but I'd like something that could give me fighting chances against 1800-2000 players.
4. e6 and a transposition to a French with the c pawn blocked in.
5.Alehkine's Defense? Wouldn't that be a normal Alehkine's after 2.Nf6?
6.Scandinavian. This is recommended in a chess.com video called "The Modern Nimzowitsch". I tried it and felt uncomfortable with my queen on a5. It felt dirty and wrong. And I even lost my queen putting it there once.
Anyway, those are all the options I could think of. Right now, I'm playing 2.f5 for no real reason other than my opponents get themselves in trouble against it, but it's not that hard to find the most critical lines. Bb5, Ne5 and black is not having any fun. What would you play, other than e5.