As title suggests, pattern analyzer Nien does a red manuver over debris ending up with a enemy ship in arc range 1. Does he get 1 action, 2 actions or no action? And ends up with no stress or 1 stress?

Apologies if this has been asked already. Search hasn't been very helpful.

2 actions no stress

It’s worth noting that any ship with PA executing a red maneuver over debris will still get the action from PA, as the stress from debris isn’t applied until after the check difficulty step.

Which by extension means that Nien still gets the PA action for going over debris even if he fails to land with a ship in arc at R1 from the maneuver, and can then boost or barrel roll to a position where his ability will trigger in order to remove both stress if it is possible to do so.

Agreed with above. The order of effects for a THREE-action turn:

1. Nien Nunb reveals a red maneuver, and fully completes the move.
2. Pattern Analyzer lets Nien perform one action... say, Focus, with S-foils closed.
   1. He is also permitted to link off of that action if allowed; in this case, closed S-Foils lets him red barrel roll, putting a ship into his front arc.
   2. Nien would then receive one stress for the red action.
   3. Nien Nunb's ability resolves for the red action, and he removes one stress token.
3. At the check difficulty step, you receive two more stress tokens; one for Debris Field, and one for the red maneuver.
   1. Nien Nunb's ability resolves for the debris stress, and he removes one stress token.
   2. Nien Nunb's ability resolves for the red maneuver stress, and he removes one stress token.
4. Finally, Nien Nunb can perform another action during his Perform Action step, such as target lock.