There’s some useful .swf help files with the download to help you get the basics of adding XML port code into your Actionscript. I guess the basic sort of info you would be feeding from Flash would be simple things like x,y position of movieclips, velocity of movement, collision bangs, that sort of thing? It should all be covered there.
It’s good to be ahead with the Max and MIDI stuff – it’s best that you have all the Max control stuff nailed for when you start getting numbers sent from Flash.
If I remember correctly, Flashserver is polling constantly so even when numbers aren’t changing you’ll still be getting bangs when you don’t want them. [change] will sort that out. Worth bearing in mind.
Keep me posted with what you’re getting on with – would be interesting to see how your project grows :)