Talk to a lawyer, get everything you’ve already thought up documented with dates.

Read the contract carefully and don’t allow them to claim perpetual licenses to anything you’ve already come up with.

You can have /home on a separate drive without any problem, it can even be a network drive versus physically attached.

Format the drive, copy the contents of the current /home, mount the new drive as /home.

/boot and /var are usually separate for good reason. The short version is: you don’t want to mess up /boot and you don’t want /var to fill up and use up all the space in / if it isn’t separate. Most of the everyday growing/changing data on your machine lives in /var.