I have a LOT of experience thinking about this question lol. I had a DJ background and couldn't understand my C from my G notes. But now, I can't live without my keyboard.

Having said that, if you're looking mostly to work with loops, I highly recommend skipping the keyboard. It's not worth your time at the moment.

You said that you'll use Ableton. As others have pointed out here, you really can't go wrong with Push 2. It works seamlessly with Ableton. If you haven't purchased Ableton already, you can get pretty good deals on an Ableton + Push bundle.

If you're on a budget, I recommend the Akai APC mini. If you can find a decent used instrument, you're looking at around $40-50. Cheap, but decent Akai durability.

Another one I recommend is Novation Launchpad mini. Again, it's under $100. Is extremely configurable

(Pro tip for Launchpad: download the drivers from this page. It really unlocks the Launchpad's potential: http://motscousus.com/stuff/2011-07_...n_Live_Scripts)

Found this article with a good overview of controllers for Ableton: https://midination.com/best-ableton-controller/

Re: Keyboards

If you're going to go down this path, I really, really recommend not splurging at first. Buy the cheapest possible keyboard you can buy at first. Something like a Nektar Impact GX49 (under $100). Don't buy anything with less than 49 keys. I know it's not very portable, but it really kills the purpose of a keyboard to have just 25 or so keys.

Don't fret about key quality at first. Just buy something cheap - and preferably, second hand - so you get a feel for it.

Good luck!