Does the Mail app store the email on the storage drive?
Some of it will depend on the type of mail account (POP vs. IMAP) but yes, the Mail.app will store your emails from your accounts on the system drive. How much space it will consume depends on whether there were lots of large attachments to those emails. There is no way, though, to selectively on store emails from a limited timeframe - it's all-or-nothing.

As a point of reference, I have emails going back over eight years for 10 different accounts and the total size of the email and attachment storage is just over 9GB. I'm probably somewhat unusual in regard to how long I hold on to emails. But 9GB for that seems reasonable and I have no problem having those same accounts synched on my MacBook with a 250GB drive.