grammar - Singular or plural in these sentences . .

I've often written sentences like these:

1. The structure and linearity here is [are?]what is [are?] stifling creativity.


2. Compare: The pencil and pen are in the room. [Where is seems wrong]


3. The project is based on chapter information and book category, which is [are?] useless when guiding you toward the actual objectives.


4. There is [are?] a table and chair in the room.



5. Compare: A table and chair are in the room

Is the is appropriate in these sentences? Especially the first one; I don't quite get the rules at play here, so am only going by what sounds right.