Have you looked at the help file for vst~? The answer to your first question was in that. It also describes how to use CC messages.
Regarding sustain commands, you have two choices: Have Max do the work, or have the vst~ do the work. In the first case, use something like a sustain object. If you don’t like the way it works, search for "sustain" in the forum to find alternatives. If you want to use the synth’s internal sustain mechanism, just make sure it’s receiving the appropriate CC command. I believe it’s CC number 64 — a nonzero value means "sustain on", zero means "off".
I’ve tried naming my GRM Tools vst plugins to have them automatically recognized on opening a patch, but I keep getting the message "can’t find…" I’ve tried renaming in the vst~ object, adding the Library/Audio/Plugins/VST path to File Prefs. Nothing seems to let it be recognized.