It is interesting opening with lots of transposition possibilities. No obvious weakening. I do wonder , how would white proceed after Na3 e5(with the threat of Bxa3). Maybe play b3?
I too think it is an interesting opening.
If you have the time and the resources to read pgn files then downloading the database book "A New Knightmare" (based upon Durkin's book of the same name) is worth your time.
As to how to proceed after 1.Na3 e5
It would depend on whether or not you would class Bxa3 as a threat and whether or not there is a chance of it happening anyway.
As a regular player of Na3 in blitz (and sometimes standard), I have noticed that the higher one's opponent is rated the less likely that Bxa3 happens. I would hazard a guess, it is believed that it is more prudent to hold on to the dark squared bishop to defend said squares rather than simply exchange it off for inflicting a perceived disadvantage of doubled pawns.
I used to play 1.Na3 e5 2.Nc4 but now I have largely shelved that because 1.Na3 e5 2.Nc4 e4! intending d5 is just simply over powering for Black
I am still out if Bxa3 is an actual issue for White but as I don't like 2.Nc4 I am trying 2.e3 at the moment and if Bxa3 does occur, you have the open b file for both your rook and Bishop b2
It is noted on a couple of website that Durkin has also mentioned 2.g3 2.c4 2.b3 and even 2.d4 as being playable (this last one, I really not sure about)
I don't think anyone could argue that Na3 is a very good move in terms of getting a strong position, least of all me.
But I would like to ask a question? 1.Na3 is only 1 move, the first move by White, just how can you conclude just how good or bad a move is if the other side has not moved?
I liked your line in first post where you played Na3 and then shifted to english with c4. So, it is basically English with an Na3. Then, castled on queenside. Nice!