Please clarify following which vs that

1. which is non restrictive modifier. can which be restrictive modifier as well when one uses it for modifying non-people nouns?

2. Parallelism question: which one is correct of these two and why. why the other one is wrong
A: Many engineers choose to seek employment in the suburbs rather than to face low salaries in the city.
B: Many engineers choose to seek employment in the suburbs rather than face low salaries in the city.

3. Parallelism question: which one is correct of these two and why. why the other one is wrong
A: The teacher is looking for a cafe where there are comfortable chairs and where there is free internet access.
B: The teacher is looking for a cafe that has comfortable chairs and that provides free internet connection
C: The teacher is looking for a cafe that has comfortable chairs and provides free internet connection

4. Parallelism question: which one is correct of these two and why. why the other one is wrong
A: They were dismayed to learn that their neighbors were untidy, disagreeable and uninterested in making new friends.
B: They were dismayed to learn that their neighbors were untidy, disagreeable and uninterested to make new friends.

5. Parallelism question: which one is correct of these two and why. why the other one is wrong
A: The joint business venture will increase employ satisfaction and will improve relations between upper management and staff.
B: The joint business venture will increase employ satisfaction and improve relations between upper management and staff.

6. Parallelism question: which one is correct of these two and why. why the other one is wrong
A: The band chosen for annual competition appealed to both the student body as well as administration.
B: The band chosen for annual competition appealed to both the student body and administration.