Does it matter how many seats I put on a table?

It is there to help your staff, and nothing is blocked by it. The seat count shows on each table on the Tables screen and at the top of an open tab, so a waiter hunting for a spot for six can see one at a glance. A booking for six is not refused because a table seats four: you decide what you can take. Anything from 1 to 40 seats a table.