I've been running 6 years on a 5x8. I have 5 zones, and cannot imagine using/needing more. However, depends on what you will be making.
For me, furniture parts are done on a non-vac region where solids are clamped/screwed down.
Cabinetry is typically 4x8 sheets = wide open on primary 4 zones 95% of the time.
Partial sheets are when the gates get used. If I have a sheet a bit off size, open more zone and use other scraps to mask around the work piece.

My first vac table attempt was running 80/20 aluminum channel, splitting the table into 6 zones and using pallets in between the aluminum extrusion grids. Sounded and looked like a great idea based on examples shown here. Ultimately, I scrapped the whole thing and ran a solid sheet of ultralight mdf "trupan" with zone division taking place in the manifold underneath. Life got way easier and so did the accuracy of my work.

I cringe at the thought of 25 zones. A very complex project that I don't mind saying will almost certainly cause more problems than they're worth.
I'm sure the common response is going to be, what exactly are you planning to produce on this machine, as that really is the ultimate question before the best guidance can be given.

Jeff