Whatever controllers you choose will most likely connect directly to a USB port on your computer and therefore require no additional interface for that.
You will probably want an audio interface which would give you higher quality sound output than what's built into your computer - but it is not required, it's a highly recommended option.
You would need an audio interface if you want to use a microphone into reason. you can get USB mics, but you'd get much better quality out of a better mic through an audio interface.
In Reason, you can setup a controller to be a 'master controller' which will cause it to always be playing the currently selected track (in the sequencer) and/or you can lock a controller to a device, in which case it will always play that device no matter what track you select.
The Combinator device will let you put multiple devices in it and then split the keyboard across those devices - i.e., you could split a keyboard in the middle and route the lower keys to one device and the upper keys to another.
The combinator configurations can be saved as patches, and the overall configuration saved as a song (.reason) file.
There are many ways to do this, but I like creating a separate song file for each song in a set, then opening them all up before the gig - that way everything is up and ready to go - you don't have to hunt for files and wait for them to open during the gig.
you can either layer them with the first one on top and last on bottom and then close them as you play through them, or use the application browser to switch between them.
HP Pavillion DV7T-3300 Laptop | i7 Q720 @ 1.6 GHz | 4GB RAM | Win7 Pro 64-bit
m-audio Axiom Pro 61 keyboard controller || iPad2 | RetouchControl DUO | TouchOSC | LoopBe30 MIDI
m-audio Mobile Pre USB (original) audio interface | ASIO4ALL || RØDE NT-3 mic
Reason 6.5.3 || Pulsar | Saturation Knob | Rough Rider | TSAR-1 | Uhbik-A | Re-Tron | Polar | Echobode | Uhbik Q | Uhbik F | Morfin XF | Uhbik S | Uhbik D | Uhbik G | CV Suite Line Processor | wbl5515 | Uhbik P | RE-2A | Radical Piano
Last edited by SteveDiverse; 2013-01-02 at 18:59.