It's a wild guess, but I'd say you'll be around or a bit below the minimum requirements. You either have the ATI Radeon HD 4850 or the 4670 (you may check that from "About this Mac" menu option). The former is the better of the two.
The Elder Scrolls Online client requires 60 GB on the computer's hard drive. At least 80 GB on PC and 85 GB on Mac are needed to perform the download and installation operations, and the computer needs about 15% of its hard drive space to be empty to run properly.
The game requires approximately 53GB on the PlayStation 4 and 59GB on the Xbox One.
Please note that the client size can change with the evolution of the game.
I tried to join ESO for the free trial but I was let down by my steam account which I have not used since way back. Well, never mind, I anyway will spend the next few months hoping my spellweaver to reach level 40 in Drakensang. I can't anyway have two major games running at the same time.