The drive can be unallocated before installing. That's the best option actually. Mint's installer (as any other OS available) can partition drives (manually or automatically).
Just leave it unallocated.
If you do partition manually, you'll want to do this:
- Create a "root" folder (/) of about 20Gb.
- Create a swap partition (double the size of your RAM, so if you have 8Gb, create a 16000Mb "swap partition". This partition does not have a mount point. Create at the beggining or end of your drive, so it's faster.
- A "home" partition (/home) of at least 100Gb (the reason to do this, is for updates or distro change, all your data and app data will be saved).
For file system you should use Ext4 of Brtfs. Ext4 is more stable, but Btrfs is better.
Install the bootloader in "dev/sda", do not choose a specific partition.
PS: Just in case it's not clear, the manual partitioning will happen when installing Linux.