recording live band

Hi all, I have just purchased an iMac and want to record my band live. I wondered, as I need max 12 channels can I do the following>>>>>>>>>> get a 12 channel interface and record directly into my 1TB G Drive mobile usb storage unit and then, download onto iMac to edit? If so a guestimate on how long I could record for?? I have no idea.

I did not want a laptop but if my idea is not possible I may upgrade my iPad as mine is an old one. Would that do the job? I have been a muso for 44 years but the owner of an iMac for only a week. Thanks in advance PeTe