I bring 6-10 keyboards on stage when I play live with the band I am in. I have three 2-tier columnar stands set up in 'U' shape (the stands are like the Apex and Deltex stands we know of). The stand directly in front of me has an 88-key on the bottom and usually the Behringer Deepmind-12 on the top. I have the height of the the bottom one where I can mostly sit, but can also stand. If I am playing the top keyboard only (Deepmind-12), I will stand.
For the second stand (to the left of the stand in front of me), those generally are keys that I have MIDIed to the 88-key in front of me. I will occaasionally play the bottom board on that tier, but not generally.
For the third stand (to the right of the one in front of me), I have 5 boards on the two tiers. The top tier keyboard is MIDIed to the 88-key on the front stand. The bottom tier has the 4 Yamaha Reface boards on it (with a custom-cut piece of polycarbonate for the 'shelf' and two 3-D printed 2-tier stands that sit on the shelf). Then the two Reface that are MIDIed to the 88-key are on the top tier on that shelf, and the two Reface units I actually play live (the Reface synth and Reface organ) are on the bottom tier on that shelf. These 'tiers' are small module stands that I have modified to be able to support the Reface keyboards. Both custom tiers sit side-by-side on the polycarbonate 'shelf' and the entire 'shelf' span about 40 inches in width. I will either stand or sit to play the Reface boards on this columnar stand, depending on my energy level and the song I am playing.
As a classically-trained pianist, I was trained to sit in front of a piano. When I started touring, I stood quite a lot. For the last 15 years or so, I mainly sit, but will stand to help with creating energy in the group and when it gets to the crowd, I will sit back down. If I am playing piano-centric songs (Journey, solo time, etc...), I will sit. I use a Rok-N-Soc seat without the back (only because I have not bought the back rest yet). It is VERY comfy and works very well. It swivels and so if I stand and play one of the boards from the side stands I mentioned above, I simply sit back down and turn back to the main stand in front of me.
When I am playing a solo piano solo during a show, I definitely sit, but I am kind of leaning over the 88-key a bit, so I can give the appearance of commanding the keys better. When I really think about it, I actually DO play it better when I am leaning somewhat over it, because it really feels like an extension of my arms and hands. I used to sit traditionally in front of my boards, and I felt like I had to reach a bit more and it was not comfy at all.
I am 50, so I am very comfy with sitting more than anything. I pretty much leave the standing like I described above, but I also stand when I break out the keytar on stage.
Because of the reach of the right hand into note ranges below Middle-C, I developed a technique to where I use the left hand to help play those as well. I have the ability to swivel on the stool, but I learned to use different fingerings to make those additional notes more accessible when needed. It also gives a neat look when someone is filming me, because watching the hands cross over or go into ranges they normally do not go into, is neat to watch. I still do hand over hand runs traditionally most of the time, but smaller runs is when I use the technique I have developed and it works for me.
I hope that this helps a bit.
Grace,
Harry