The problems with _only_ owning a synth with "mini keys" (like the MicroKorg or its variants):
. . . (a) It's difficult to control dynamics (loud/soft) on mini keys, and:
. . . (b) When you get a keyboard with full-size keys, or a piano, all your "muscle memory" will be wrong !
So the "two-keyboard" idea (with a 61-full-size-keys "main keyboard") is a good one.
As I remember it, some of the low-end Arturia synths (microBrute, etc) don't let you save your patches (configurations of knobs and buttons). IMHO that makes them unusable for "live" playing (where you must change sounds from song to song), and very tedious for studio work.
The microKorg and its more-powerful cousins (microKorg XL / XL+) _do_ let you save your patches. And they interface nicely with computer-based "patch libraries" and "patch editors", which make sound-editing _much_ easier than it is, using the instrument's own knobs.
(I have mixed feelings about my microKorg XL+. Quite flexible, but not easy to master, either from the front panel or via computer. Too much flexibility, not enough knobs. An UltraNova or MiniNova might be easier to get one's head around.)