You need to consider how you are going to get your captured video onto your 10TB.
I don't know anything about Raid storage but normally an external drive would be formatted to OS Extended ( Journaled).
You might want to research this before getting too far in.
When you capture your tape it would be ideal to capture straight onto the external drive. This way you just take your drive over from the old Mac to the new Mac.
This is quite straightforward to do. You just need to consider the cables needed to connect the drive to the Mac.
As you have a new Mac you will have iMovie ver 10 on it.
Depending on what OS your old Mac is running ( Mavericks or later ) you may be able to download iMovie 10 on that older Mac, or you may have it on there already of course . If you do not have it already get back here for more info.
The reason you may prefer to capture to iMovie 10 on your old Mac rather than say iMovie 8 or 9 on your old Mac is that the format it captures in is different , assuming that you have recorded in HDV rather than DV.
iMovie versions 8 and 9 capture HDV in what is called Apple Intermediate Codec. In other words what is on the tape is transcoded. This is not a problem as it is still high quality but this has to happen in order for these versions to edit.
In iMovie 10 transcoding does not take place on capture, what is captured is basically a copy of what is on the tape ( MPEG).
This version of iMovie can edit this native format. It can also edit Apple Intermediate Codec files if these are imported.
If you can run iMovie 10 on your old Mac AND capture your HDV in this version then it would make sense to use this version , and transfer the files over to your new Mac if you want to.
Another benefit is that the native MPEG takes up less storage than AIC .
If you cannot use version 10, on old Mac, then you can use the AIC import from 8 or 9 in your version of 10 on the new Mac.
Or you may decide to use the captured AIC from 8 or 9 in 8 or 9 directly, and edit there.
Let us know what versions of iMovie you have on the old Mac and the OS.