A Linux Mint operating system takes about 15GB and grows as you install additional software. If you can spare the size, give it 100GB. Keep most of your free space for the home partition. User data (downloads, videos, pictures) takes a lot more space.

How much space should I allocate for Linux?

A typical Linux installation will need somewhere between 4GB and 8GB of disk space, and you need at least a bit of space for user files, so I generally make my root partitions at least 12GB-16GB.

Is 100GB enough for Linux?

100gb should be fine. however, running both operating systems on the same physical drive can be tricky due to EFI partition and bootloaders. there are some strange complications that might happen: windows updates can overwrite on linux bootloader, which renders linux unreachable.