Is there a limit to the number of features, apart from space?
There is a limit of 1 Major Focus, but it doesn't say anything about features.
None that I am aware of. I like to stack them on 
Can you have the same feature multiple times then? A medical lab with several pallets, a scriptorium with several desks - do they each provide a bonus?
I was under the impression you were limited to 1 major and one minor, which had to be differing items. If you are allowed multiple desks that could be quite interesting... with enough space you could transcribe truly massive tomes in a single season.
It's there, just subtle. Look at page 113 of Covenants, Laboratory Virtues and Flaws, second paragraph, "Most laboratory virtues and flaws can only be taken once -- those few that can be taken multiple times are marked with asterisks in the list below.". Then, look at Major Structure Virtues, Page 113, Covenants, Greater Feature*. Look! Asterisk! So it can be taken multiple times, as opposed to Greater Focus, which has not asterisk, and can only be taken once. Mind, the wording of the virtue argues against stacking the SAME focus, using the word unique, which I think we all agree, stops once you've added another desk or pallet.......
That seems fair, If you want to stack the bonuses up you can easily imagine creating multiple features that do similar stuff.
e.g. if you want crazy high bonuses to Animal, stick in some large animal cages as a feature, a vivisection table, a large collection of anatomical drawings or tapestries, maybe a magic item that creates animals with a day duration (for experimentation). The last would be a magic item but the rest could all be features, and one could be a focus.
For experimentation, Moon duration tends to be better. Much more flexible.