(b)
Homonyms, such as “cell” in biology, electricity, or prisons, should not be a problem, since each is encountered in its specific subject context, where its local meaning should be clear,
(c)
How do we distinguish between the operation “building prefabrication” and the entity “prefabricated building”? In a classified catalogue these might be distinguished notationally. For example the first topic could be expressed by linking the two facets as “building-prefabrication”, and the second (adjectival) topic as “building (prefabricated)”. On the Web, with independent facets, this cannot be done. It is probably best to treat “prefabricated building” as a subclass in the buildings facet.