Just one more pointer - in case it isn’t obvious: a rack doesn’t need to consist on one plugin only. My piano rack, for example, consists of two main plugins (Pianoteq and Addictive Keys), plus a number of refinement plugins (EQs, chorus, compressor, and a main volume plugin). For any given rack state, only one of the main plugins is active, and a selected set of refinement plugins. Only the volume plugin is always on, wired to a MIDI assignment (CC #7).
Another hint: racks don’t need to have just one stereo pair as input: my main “volume & fx” rack has three inputs:
- Main In —> all racks’ output is sent there
- Reverb in —> goes to the reverb within the rack
- Delay in —> goes to the delay within the rack
For each rack, I set up to three audio routes: one always to “volume & fx rack, main in”, but depending on requirements, also additional ones to “volume & fx rack, reverb in” and “volume & fx rack, delay in”, controlling reverb and delay levels by the individual levels of these routes. Since I control the rack’s level using the rack level fader, these “sends” are automatically “post-fader”.
I usually set my “volume & fx rack” state using some typical rack states, which look like “main reverb + 1/8 delay”, “main reverb + dotted eights”, “honky tonk bar reverb + quarter delay”. But sometimes, I want to customize the rack’s component states individually per song (some exotic combination of reverb & delay settings). That’s when I use “exported states”, which allows me to set the individual states for the delay & reverb plugin within the song (just open the rack, set the individual states - with “exported state” rack behavior activated - and close it again).
But now we’re really getting into some of the hidden magic 
Cheers,
Torsten