I'm a newb so not much advice/perspective I can add other than to say, I had Plaits suggested to me for my setup, which also contains Maths/Dixie/Quad VCA, and I've been loving it.
e.g., Dixie pulses enveloped via Maths and used to trigger the percussive modes of Plaits gets some interesting ambience, if you play around enough.
With the firmware update, Plaits has an LFO mode, which paired with Dixie gives you good flexibility if you want one to act as the clock for the other.
Someone also suggested (to me) a chaos generator like Wogglebug to add an element of unpredictability, if you have room for it. Not essential but something fun to keep in mind. Ambient, in my experience, thrives on chaos.
FX Aid pro kept coming up in my search for FX, so sounds like you can't go wrong with that recommendation.
Good luck, have fun, and seriously consider wise people's advice when they say, "You may need a bigger case."
I started out with a 64 HP "budget setup" that quickly ballooned to 128 HP despite everything I could do, lulz.
While I'm very happy with a smaller setup, too small a setup might not achieve all the things you want, particularly polyphony.
Here's a link to a good thread from the forum on why polyphony isn't easily achievable....item #4 in particular.
Best wishes, good luck, and enjoy the ride! :)
“You must have chaos within you to give birth to a dancing star.”
― Friedrich Nietzsche