I've been wanting to get into this for a while now. Do you have any groups you'd recommend? Solo study has its limits. :)
The below forum is pretty much ground zero for the hobby in the United States IMO. There's some very very talented regulars there who are truly pushing the limits. All the owners of the electronics and software used in the hobby are on this forum too and post regularly. Many University teams show up on this forum too, i believe this USC team is there from time to time asking for advice.
https://www.rocketryforum.com/
this thread in particular is fascinating, a build thread for a 2 stage rocket that eventually hit about 150k feet
https://www.rocketryforum.com/threads/workbench-2-0-two-stag...
Here's a post with some nice pictures of the rocket, launch, and apogee
https://www.rocketryforum.com/threads/workbench-2-0-two-stag...
Mostly it's getting everything to go right a the same time. Fin flutter destroys rockets, so does wind sheer, so does bad flight controllers or bad programming. Parachutes not deploying properly in low pressure high altitude flights, second stage igniters not working as fast as they should at low pressure, the list goes on and on.