Yeah you can opt for a 240-ish GB SSD for Windows or if you want to play it safe you can go woth a 480-500 GB SSD for very little more.
1TB SSD for your games will do and be a good middle-ground in terms of storage performance without breaking the bank.
OPTIONAL
If you want to split FS you can do the following:
- Install MSFS (Microsoft Store) in the default C: path.
- Run MSFS, it will prompt for Package location.
- Install/point the “Package” to a custom location on your game drive.
(example: D:\PC Games\Microsoft\MSFS\Packages)
I only do that to avoid the Windows store app clutter and permission issues on my game drive.
It just happen to also allow me to Repair AND Reset the game (MSFS app settings) without it requiring a full 100+GB download again.