I have a 1080 and have tried 4K via DSR in the PU, and while it looks nice, the framerates are cr*p. Hopefully that will improve as the engine tweaks are implemented, but I am not expecting to be able to run the game happily at 4K.
An external drive probably won't be any quicker than your internal drive. If you want speed, you want to add an internal SSD drive, but they aren't as cheap. You can have fast or you can have "very low budget". If you don't know about PC's, specifying the rest of your PC setup would help us.
I have had it on my radar since this reddit thread 8 months ago: https://www.reddit.com/r/starcitizen/comments/4jazc3/is_it_me_or_is_this_the_exact_copy_of_star_citizen/ It will be interesting to see how it has come along when it hits early access.