Disregard any responses that proposes to answer this question definitively .

Using the information that you've given: 1) you're primarily a guitar player 2) you have limited keyboard skills 3) you want to easily put together 'quick-and-dirty ideas 4) you like the concept of on-board sequencing; I would suggest that you initially abandon the synth/workstation approach and go with an arranger workstation (I think an arranger keyboard IS a workstation when used in this way). You could consider an arranger module (Midjay) since you already have a keyboard controller. Personally, I agree with Chony in that if it is to be used only in the studio, why not just leave it permanently hooked up to a computer with all the fore-stated advantages that that offers. There are many full-featured, inexpensive sequencers (ie Reaper) that will easily handle both midi and audio. That would also open up programs like Band-in-a-box, etc. which could be useful for a non-keyboardist. JMO.

chas