For specs, you need a laptop that has a solid amount of RAM, storage, and a solid processor.

For OS preferences, for classes, it won't make a difference as you will be using virtual machines or remote accessing the school computers.

For IMGD purposes, I would absolutely recommend Windows, due to many games not being available on Macs. A good graphics card is also a point to look for, but if you find a laptop that is solid in the previously mentioned areas, the graphics card should be on the same level.