I second the suggestion to go with a 27" iMac. the refurbished store usually has some pretty good deals and you will get more for your money. in fact, even though my most recent purchase was a 15" retina, I am still envious of the beautiful 27" iMac. Besides, no serious work should ever be expected to be performed on a completely mobile setup (with exceptions for broadcast journalism and related fields)
the reason i got my rMBP was that it had higher benchmarks than the iMac that was in my price range, and I needed a laptop to replace my older late 08 MBP for when clients require me to work on site. I already had a current gen Mac Mini for use at home with my 2 large monitors, so it made more sense to upgrade my mobile setup. that said, as soon as i got the rMBP, i no longer found a viable need for my Mac Mini, since I prefer working with the rMBP attached to my monitors so I can utilize the discrete graphics for 3D ray traced After Effects rendering, and it is quite a pain switching a bundle of wires between 2 machines. Plus, trying to keep up with updating software and plugins, as well as project files on 2 different hard drives is a pain as well and it makes keeping backups all the more difficult. I considerred keeping the Mini around to use as a render box, but that seemed like more effort than it was worth and it was too much of a luxury to justify not selling it. Also, it would have required me to keep an extra monitor attached, as well as another keyboard and mouse.
All that, to say, you can do basic edits on any number of machines. HD is not as demanding as you think (4K is a whole different story though). You can use what comes with whatever computer you end up getting and be satisfied. Eventually, if you are serious about it, you will want to upgrade some of your setup. Thats when bigger, faster drives, maxing out ram and adding additional monitors or peripherals comes in. Industry types will swear up and down you need nothing less than a RAID configuration and workstation graphics in order to edit. Independent freelancers like myself will insist on more of a refined, middle ground setup that gives you more options and makes your life easier in certain aspects. But the truth is, for someone starting out, all you need is a computer made within the last 3 years to edit video comfortably.
oh, and just to brag, i wanted to mention that i got my 15" retina from the refurbished store for $1600, which, for the 8gb RAM model i ordered, was around a $500 discount from new. When i got the computer though, i discovered that it was actually a 16GB RAM model, making my purchase through apple's refurbished store an $800 savings over new retail. so the moral is, always check the refurb store first!