New to the forum and still somewhat new to the iMac world. I have a late 2013 27" iMac, 3.5 GHz Intel Core i7, 16GB memory, and a 3TB fusion drive. The drive has been filling up quickly with lots of photos and video. I do some very amateur editing with Final Cut Pro X. I'm looking to add an external drive that will remain connected/active. I would transfer photos/videos to that drive, and access them when viewing or editing, leaving everything else on the built in drive. I am hoping this can be accomplished without noticing any delays while accessing/editing. Is this possible? And if so, can it be done for around $300-400 (or less)? I think I would prefer 3TB or 4TB external. I'm guessing some sort of Thunderbolt setup would be my best option? Please provide any suggestions. Thanks!