I reccomend you use this template:
https://www.logicprohelp.com/forum/viewtopic.php?f=9&t=143416
The other comments you make about peculiar behavior, however, is related to LogicPro and the way it works with multi-instruments.
LogicPro is setup so that you can create up to 127 tracks feeding into a single AU3 multi-timbral instrument. That single multi-timbral instrument is hosted in a single instrument channel. So.. 127 seperate tracks, all feeding a single instrument channel.
Whenever you hit the SOLO/MUTE buttons on any of those 127 tracks, it effects the same instrument channel, that's why they are all in sync with it. Hitting solo or mute, effects that single instrument channel they are all funneling through. The fader on the track header also effects the volume of the one single instrument channel.
VePro.AU3 is a multi-timbral instrument, sitting in one instrument channel, and servicing up to 127 midi source tracks.
Likewise, Scripter sits on that one instrument channel. So that means all 127 source midi tracks have to funnel through that one Scripter script. If your script is smart enough, it can take that into consideration by handling all processing per channel and port. A lot of scripts floating around do not make any attempt to distinguish channel and port, so they are just doing it globally to all midi source tracks that are funneling through it.
So.. That is to be expected, the only solution is make smarter Scripter scripts... if you want to have more then one source track fed into a single multi-timbral instrument.
And with VePro, the only way to feed those 127 source tracks to a single VePro instance, is to funnel into a single instrument channel, as described above.
So yes its solvable, but generally involves more complicated script programming.