Equalizer, I have been considering some of the same issues, so maybe you will find the following helpful or maybe someone can give some suggestions.
I have a laptop and music software. Unfortunately, to make music, I have to attach the laptop, laptop power supply, controller, audio and MIDI cables, boot the computer, and launch the music host application. Sometimes, the Muse does not want to wait that long!
My current thinking is to replace the controller (an Oxygen8) with a small, lightweight synth that I can use with and without the laptop. Two octaves is too limiting, four is ample, and three might (I'll have to try to know) be an acceptable compromise between size and range. (I can always MIDI my 76-key Roland A-50 when I need more range).
I am still deciding on which small synth to buy. There are some inexpensive alternatives: used Roland Pro-E, microKorg, Korg MS2000, used Korg Prophecy (kewl, but mono), Novation KS4. Any other suggestions?