Gapps crashing more than likely isn't a twrp problem, but I'll still check on that if you get a log. GSIs shouldn't be hanging though, and that probably is a twrp problem, unless it's just a simple user error. I personally haven't had any problems. I'd appreciate some logs so I can see what's going on. It might be something stupid, or it could be something much worse. I should definitely check it out in any event.
For the twrp related logs, don't flash gapps or magisk. Just do your wipes, flash the GSI, then see if it boots up. Some GSIs take awhile to boot. Havock OS does. I recently tried that one, and I swear it took like 7min, but it did boot up and work. Definitely give it a good 5-7min, then grab a log if it doesn't go anywhere. Not flashing magisk or gapps will make the log much easier for me to read and help narrow down the GSI specific issue you're having.
Edit: What model is your phone? Also, you should try using the latest twrp I just posted.