What is best method to archive movies?

Appreciate any advice as to how to best transfer my iMovies off of my MacBook Pro running Mtn Lion, to an external device (thinking of a 1 or 2 GB G Drive) for archive purposes. Once my old VHS home movies are transfered & digital on iMovie, I'll edit a bit in "Project" & finalize them. I want to send both the final Projects & original film (Events?) to an external HD. I'm thinking of getting a 1tb G-Drive mobile as easier to move around BUT if someone feels it's more important to get a desktop G-Drive for video, due to having a fan over the mobile, then I would like to know before I make the purchase. In that case, I will go for 2 or 4 TB. I don't plan on editing from the external HD, I only want to archieve my movies there BUT also want the ability to move them back into iMovie in case I want to share them with someone. I assume that would have to be done via YouTube, which I have already used. Thanks for any tips. Pls note that I'm not computer savvy so no big tech terms; pls treat me like I'm in kindergarten with any replies! 😉 Tks! -Lynn