A lot of the functionality of a given MIDI controller depends largely on how things are setup in your DAW of choice ~
Which in your case, sounds like it’s going to be Reaper.
You’ll probably want to download the Reaper manual and take a look at the section covering the step sequencer. That should tell you what computer keyboard controls would normally be used for editing, stepping, etc., and if any of the controls can be mapped to MIDI commands.
With the exception of some MIDI controllers that are dedicated to specific software packages (such as the Akai APC-series controllers, which are hard-wired to specifically support Ableton Live), most MIDI keyboard controllers are pretty generic, with the basic controllers (pitch wheel, modwheel, keys) sending basic MIDI messages that would be pretty much the same on any keyboard.
Most MIDI controllers in the $100+ range (and some even cheaper than that) come with multiple controls that can be programmed to send specific MIDI commands that you specify. This can come in REALLY handy for interacting with your DAW software, AND for directing controlling your synth gear.
Keep in mind that if you want to control Moog synths without using a computer in the mix, you’ll need a MIDI controller that has conventional 5-pin MIDI DIN output ports.
You CANNOT connect a Moog synth (or for that matter, any other synth module that I know of) directly to a MIDI controller that has only USB. You would have to connect both pieces of equipment to a computer or other USB host via their USB connections, then route the MIDI data between your devices via software. Sounds complicated, but really isn’t that bad once you get the hang of it.
My advice, FWIW -
Spend the money and get a decent controller with at least 37 to 49 full-size keys (a controller with fewer and / or small keys can be outgrown in a hurry), and as many programmable controls onboard as your budget will allow. Novation , Akai, Roland, and many others make some nice, durable MIDI controllers that would probably suit you just fine.
My primary controller is a 49-key Novation Impulse, which works great, but “ain’t cheap” - and was well worth the investment, in my opinion.
It works great as a custom controller - along side my iPad running MIDI Designer - for my software and synths.
Also, I HIGHLY recommend you dig in and start learning MIDI ~
Once you start dealing with DAWS and synths, MIDI becomes a very big part of how everything works together, and you’ll want to learn as much as you can to really take advantage of all the capabilities of your gear. You don’t necessarily have to learn about HEX code, SYSEX etc - just concentrate on the basics that involve keyboard note messages, program change messages, and perhaps most importantly, CC (continuous contoller) messages, since these make up the primary commands you’ll be dealing with when working with programmable MIDI controllers.
This might help:
http://tweakheadz.com/how-to-get-started-with-midi-and-the-difference-between-midi-and-audio-is-explained-along-with-many-other-core-concepts-for-building-a-home-recording-studio/
Good luck, and most importantly, have fun!!
Randy
PS -
Should you decide to include an iPad in the mix at a later date, I know for a fact that a template is freely available for the MIDI Designer Pro app that will control all of the MIDI features of the Slim (and Little) Phatty.
A template for the Minitaur is on the "to do"list … 