Hi Marshall,
Since I seem to be in a similar place as the one you describe, I'll add some of my thoughts. I was a guitar player for many years but am now very limited in what I can play due to a medical condition. I never played keyboards. In composing music now I've been using MIDI Guitar to play in the very simple (and rough) motifs I come up with, then heavily editing the MIDI before finding VST instruments to play them. Since DimPro and many free or low priced soft synths offer lots of electronic sounds for this, I've been getting into the sample libraries for the realistic instruments I want like saxes, basses, and also guitars, which I need because my playing is so weak.
I've not taken the Kontact plunge yet but have looked at many sample libraries and recently purchased a couple of Ample libraries and also Real Guitar instruments. Here are some issues I've run into, some of which may have answers that I've not yet found:
1. When I use MIDI Guitar, I'm still trying to figure how to successfully and reproducibility record guitar articulations like pitch bend, slide, hammer on. There are lots of settings that I'm working thru and I'm still learning. But without these, my MIDI guitar parts don't sound real. (Even tho much of the MIDI guitar info claims it does this, I'm still not there somehow.)
2. Once I figure out 1, I'm still not sure the recorded part will correctly fire the corresponding Ample articulations, since Ample produces its articulations with proprietary keyswitches. So coding these into the MIDI manually or playing them in afterwards with my keyboard controller (I can do 1 or 2 fingers) seems like my only choices so far. I'd like this to be more seamless but fear it won't be.
3. Every other sample library, Kontact stuff included, seems like it is going to have the same issue. If you buy a sax VST, the needed articulations are sax specific and the key switches are proprietary to that VST. A skilled keyboard player with both hands can play these in using the VST instrument's split keyboard layout, key switches in one area, parts in another. But I don't understand how MIDI Guitar can be used to full advantage if you want to play them in that way.
4. Basses can be an exception if you don't need slapping or stylized articulations. Straight MIDI can work and many of the non-sample soft synths, even DimPro, can produce decent sounding bass sounds in many contexts. An orchestral bass part might be different tho.
Sorry this raises more questions rather than answering them. But maybe others with more experience and similar circumstances will be able to offer input on the above.