Media management

I have a new JVC GY-HM750U that shoots on SD cards My question is: After I get back from a shoot I connect the camera via USB to computer and download clips which are saved to an external HD. This is eating up my available space these shoots are averaging 20 to 30 GB per event. I have been watching some Training DVDs produced by VTC which discusses hooking a camera to the computer and logging and capturing what you need thru final cut pro and firewire which becomes the original clip you edit from and those edits are linked to and you discard the rest. I am missing a step with my camera or it is not capable of doing that. Because if I do what I have been doing, ingesting the clips into Final Cut after downloading to ext HD and then produce my highlight video or feature length video and then erase or trash those originals on the external HD you know what happens you get the media lost icons. Any suggestions? I have consulted my manual for the camera however, I have not found any information on using it to play clips through in the manner the VTC tutorials have discussed.

I am having an even bigger problem with shooting with multiple cameras one is an older JVC that shoots in HDV 720p format on mini DV tape I have purchased a Firestore device for that camera. The new one JVC 750U is 1080I and I am using Go-Pros now that also shoot in 1080I They however can be changed to 720p, I believe. I have been using the new camera the 750U 1080I the most because it is new and tapeless and the go pros. They are not playing well together when used in the same sequence, I am told it is a codec issue.
Suggestions.

Thanks,
Tony