Yeah I think that would be okay. If you find that you're running out of space, or small changes like clipping and resizing are starting to slow you down you could always turn off background rendering, but with the hardware you'll be working with I don't think that'll be an issue.
In terms of external backups, I agree with SteelFlyer. I believe by default they're configured with RAID 0 (striping), which means it'll have a nice performance benefit. You can also configure them for RAID 1 (mirroring) so that if one of the drives fails, you still have your data on the other. Of course if you want to save some money you can always do what I do and just pickup a cheap 2+ TB external for less than $100. The chances that both my external and internal drives would fail at the same time are slim to none, and even if they did, I'm sure I can live with losing 3 minutes of edits.