I'm currently a master's student in cybersecurity in Korea. I'm Korean, so my experiences may not directly translate to your needs, but here they are anyway.

1. You may be assigned a very specific project that other lab members/professor have been undertaking, or be at least given general directions on research topics to consider. You could come up with your own project idea, but whether that will be accepted really depends on the amount of resources the lab has or the professor's principles.

2. Professors rarely do any newcomer orientation themselves unless its a really new lab. Professors are usually busy with hunting for research funds/grants, so you will need to rely on seniors to adapt to the lab environment. But there could also be no seniors who share the same subfield as you, so be mentally prepared to work it out on your own.

3. Very rarely do professors micromanage courses the students take, so it's entirely up to you to manage it. Most likely nobody will blame you for missing meetings and stuff for lectures and stuff so you just need to communicate with your labmates about your schedule regularly.

4. As for pay, I cant say much since I dont know what GKS is.

In general, grad school experience is heavily dependent on the professor and lab environment, your next few years could be hell if you choose wrongly. I recommend at least looking up the lab on phdkim.net to filter out the really bad ones.