Are the culture and seeding racks strictly necessary?

The culture rack is not indispensable, but is very helpful for having an organized experimental setup if several P3D chambers are being used simultaneously.
The use of the seeding rack is strongly recommended to hold the seeding circuits upright in an adequate position.

Do the seeding circuits include P3D chambers?

No. P3D chambers must be bought separately.

Can the seeding circuits be reused?

Some of their components do not admit conventional ways of sterilization (autoclaving, ethylene oxide). Hence, reuse of the seeding circuits is strongly discouraged.

Why short- and long-term seeding circuits?

Short-term seeding circuits should never be used longer than 2-3 days. Thus, they are indicated only for seeding experiments, or for experiments with very short culture periods.

If culture is being done after seeding with the same circuits, long-term circuits are strongly recommended.