Please suggest chairs to go with my Cado!  

I've seen glass-front credenzas
nothing strikes me as 'odd' about low placement of a glass-front cabinet (glass doors & shelves are almost always tempered glass, by the way). I think the system would look more balanced that way.
Would heat harm the cabinet, were it sitting around the top of the duct? I wouldn't THINK so-- the heat emitted from that duct isn't like a furnace blast, is it?

The Diplomat chair by Juhl...
The Diplomat chair by Juhl is a good shout. Something like the Kai Kristiansen chair would look nice in my opinion.

Here is a version of shelf position.
And a chair choice.
I often see original brochures that show set-up variations.
Your glass unit seems too deep to be so high?
Nice unit. I would not be so concerned about the heat source unless it is
the only one and gets very hot.

Even in the photo above,
i think the two upper staggered cabinets are an odd placement.
The lower run feels correct.