Hi Rhuumz,
My one year bonsai anniversary is approaching so I feel honoured to share with you my vast wealth of experience!
For the past year I’ve approached this patient hobby in a number of ways (not always patiently).
From reading your post it looks like you’re approaching this the right way with research, patience and enthusiasm. I am also somewhat introverted and do not enjoy the idea of participating in a bonsai club. To help combat this, the resources on the internet are invaluable as you have no-doubt discovered.
Having advanced stock would be great, is it will allow you to practice aspects of styling bonsai which you may otherwise not get to try for a long while. Advanced stock may be daunting if you’re not confident. First thing is to get confident in your routine for keeping the plants alive and understanding their requirements and being confident in your knowledge. (Which I am not quite there yet! lol)
My suggestion would be plan long-term, collect a number of varieties, which are at a variety of different stages in their bonsai development. This will help keep you busy doing different things and not just waiting for younger plants to fatten up.

This will also teach you a variety of techniques and through you straight into the deep end.
I have been lucky enough to have access to private land, which I have been able to trunk chop and train natives in hopes of collecting them in the coming years.
I have also attempted air-layering on some interesting branches in my parents backyard!
A combination of these things should keep you actively looking forward to the next stage and challenge!
Always happy to answer any of your questions if you get stuck!
Cheers,
Evenings