So far you’ve jumped a big hurdle so keep moving forward. Shadowing a PSM for several performances would be a gift to you and letting you get an idea how different each performance runs. Just shadowing one performance can be done looking at different YouTube videos, really.
Establishing relationships with people already doing the work you wish to do will create opportunities if you show you’re committed. Just do the work and gain experience on different levels of stage management - community theater, high school productions, etc. Trust me, dealing with these scenarios will help you once you’re working on bigger scale projects. Everything teaches you something. If the big shot PSMs know who you are, they’ll think of you when an opportunity arises AND never say no to anything. You’ll never be ready so just jump in to everything and trust me, you’ll figure it out. That’s where the pros toss in the famous “fake it till you make it.” Those that say “oh, I’m not ready yet” never get anywhere.