I'm not quite sure if you'll need Max 7 or not. You might have to download it and point Ableton's Max preferences to that version but you don't need a Max 7 license. Last time I looked, it did work with Max 6, but that was before I added the custom UI which is a Max 7 feature. It should fallback to the standard UI controls though I would think.
I use an external max patch for routing sysex via UDP. It works well, though this being my 3rd editor that needs an external patch I'm planning on consolidating it into a generic patch that can add an arbitrary number of sysex-udp tunnels so they can all run through a single patch instead of one per editor.
I just finished the randomize patch function so I'll be sending out the first test version shortly.
Cheers,
Joe