I have come from a similar background and I play majority live with some very occasional home studio work.
The difference between the units is:
- The only advantage of the stage is form factor all have the same functionality. However the Rack and Toaster are way lighter and more convenient than a regular amp so you are winning already over a conventional set up.
- The only advantage of a separate power amp is stereo.
For me a powered rack and remote is perfect. I turn up to a gig, I have 3 leads...power, speaker cable and remote cable. No faff with power at the front of the stage because I don;t run outboard effects. I replaced my heavy ENGL head and massive pedal board with a rack with my wireless inside plus the remote and couple of expression pedals.
Because its powered I can use the in house/festival 4x12 if needed or take my Kabinet/s. I like it at amp height as well for any last minutes changes.
So with a powered rack I can run anything - powered monitors, unpowered, FRFR, guitar cabs, Kabinet all straight out of the box in one unit. Perfect!!!! Its just not as compact as the stage.
However you can't go wrong....all of them can do the same thing its just what you personally prefer. As I like to have my cab behind me on stage, running xlr's from the stage back to an amp and cab seems odd to me BUT very doable.
Couple of other comments:
1) I don't tweak at gigs. No need, the sound is consistent ( no mike placement variation or valve inconsistencies - yes room variance but I let the sound engineer manage that). The only change I make is on stage volume at sound check then done. Also sound engineers will love you because the monitor sound is not linked to the FOH signal ( unless for some bizarre reason you want it to). So, plug mike lead into Kemper, hit a chord, sound engineers goes " yep got it" and done for level check. Easy!
2) Does it sound any good? In my 30+ years of playing I have always been looking at the latest gear etc. I've had my Kemper 6 years and not looked at another amp since.
3) It is massively flexible and programmable with so many 1 touch features e.g. turn volume pedal to zero and auto switches to a silent tuner. Wah can be set to touch sensitivity so no clicking on and off.... morph is an additional feature where you can set another set of values to switch between without a separate "patch" e.g. I use it to boost for riffs, whilst I have a totally different setting/patch for solo's...
4) The workflow is closer to an amp than other platforms ( e.g. Helix and Ax) IMO. Its not a technically scary.
5) need you live sound recorded in a studio? Plug an XLR in and boom...there is it!
Hope that helps...
BTW the Johnson Millenium JM150 Digital amplifier was cutting edge and sounded good! I remember wishing I could afford one when they came out.