We recommend that people use VirtualBox. Recommended OS’s for use with virtualbox: Kali Linux -OR- Ubuntu. It doesn’t matter as you can download Kali’s tools on (nearly) any linux based os.
Binary Ninja -OR- Ghidra. Though read on how to install Ghidra properly without the back door.
For resources pertaining to Linux and networking: OverTheWire it is suggested to start with bandit. The first couple levels pertain to linux and get increasingly more difficult. Make sure to utilizes the commands that are recommended and remember that Google is your friend. You only learn by trying harder.
Other CTFs: ask in Discord.(The Club has a team that regularly competes)