The Little & Slim Phatty's have VERY extensive MIDI implementation, and everything you want to do can definitely be done by MIDI.
(And a whole lot easier than using SYSEX, commands, IMHO...)
Assuming you have Stage II with the latest official firmware release (OS v3.1) - be sure to check out the Manual Addendum for all the latest MIDI capabilities. (you can get a copy from Moog tech support of it wasn't included with your LP).
It sounds like what you're wanting to do would be a PERFECT use for a MIDI interface-equipped iPad and a customizable MIDI controller app like MIDI Designer (my preferred!) or Lemur. Learning to use either of those apps would probably be considerably easier than learning to write & debug SYSEX commands!
Here's a thread where I discussed a MIDI Designer template I built that accesses ALL of the MIDI-controllable features of the LP & SP.
It does a lot more than you probably need, but it can give you an idea of the capabilities:viewtopic.php?f=7&t=20127&hilit=MIDI+designer
Keep us posted on your project -
MG-1, Little Phatty Solar CV, Minitaur, Slim Phatty (x2), MF-101, MF-102, MF-103, MF-104M, MF-105M, MF-108M, CP-251, Animoog, Filtatron...and some 5U modular and Doepfer stuff...