@1MANBAN I’m just a gig performer user myself a bit younger than you, but still with grandchildren. You are describing both routing your guitar through audio effects, which is fairly straightforward to accomplish with Gig Performer, but also of deriving MIDI note data from your guitar playing, which can get a bit more tricky. But these are not really things Gig Performer itself will do as I think you realize, that’s going be done by the VSTs you host in Gig Performer.
I know there are many guitarists using GP maybe they can recommend some VSTs that will generate MIDI? You might also want to look into getting a hardware “MIDI bridge” detector added to your guitar, but I know they are quite demanding of playing technique to get good results from. I’ve never heard a guitarist rave about one.
As for bass range notes you may want to take an audio only approach and use something like a sub octave plugin to accomplish a bottom end to your bottom 4 strings? This will have the advantage of following your playing much more closely, but being in tune will be critical. The process of detecting MIDI notes accurately especially in low frequencies can introduce latency which you probably don’t want.
As far as triggering other instruments from particular strings, Gig Performer doesn’t help with that specifically but two ideas occur to me: you might be able to use a really sharp almost crossover band pass filter to “catch” those particular notes and feed that audio to a MIDI detector then on to a synth. But again the latency might be a problem for you, especially if the low notes are really short. May not detect the note correctly much of the time.
Another approach you might want to consider is a live looper type of setup where you have your percussion and bass notes recorded as MIDI file loops and you improvise with those looping in a pattern you arrange. This would solve the problems of low note MIDI detection etc and would also give you obvious flexibility in accompaniment sounds.
Of course Gig Performer can give you a customizable looper scenario beyond the dreams of drummers just a few years ago. We sure have seen a lot change since AM radio was where it was all at!
You also might want to have a look at this thread: