Pretty easy:
System Preferences > Sharing > File Sharing
Under Shared Folders, you can click on the plus to add the entire secondary drive, or specific folders
You can configure the access options and also choose to share it via AFP / SMB / FTP. If it's all Mac over there, then you could just go for AFP. SMB will be for inter-operability with Windows
I'm not sure about Back To My Mac - have a .Mac account but I haven't used this feature cos I only have one Mac