I have the Pschopsis Mendenhall and I grow it differently than you probably want to grow it. Mine are in a red lava rock/limestone mix and a basket pot, watered very often, and, during the winter, put in the terrarium. I killed the last one (that I had grown for five years) when I first began growing under lights because I did not water frequently enough (it was also in rock/basket pot). The new ones are quite small and about five/six years from blooming under my growing conditions, based on my experience with the last one.
I grow with the same light as my Cattleyas (as I do most of my orchids). These seem to need a little more water than the Cattleyas (also in rock).
The Mendenhall seems to put out new pseudobulbs every four to six months for me. From experience with the last one, when the leaves get a certain size, the roots that the pseudobulbs generate will be thicker than when the plant is younger.
I have seen the mature Psch. at orchid meetings, in bloom, but I cannot remember quite how large the leaves were...I just know that my little ones have a long way to go. Hopefully, someone else can give you an idea of how large the leaves get.
These stay in bloom a very long time, sometimes years, as they are sequential bloomers.
Hopefully someone else who can answer your questions better will do so...someone who did not kill one of these in the past.