and after that I would fill in the gaps to make sure that no point along the wall lines would have a space no longer than 6' between receptacles?
No, that no point along the wall is more than 6' from a receptacle, in either one direction or the other.
Start at a doorwy; the first receptacle must be within 6'. The next one must be within 12' of the first one. The last one must be within 6' of the next doorway.
Picture yourself trying to plug in a lamp with a 6' cord. As you move along the wall, just as you move 6' from the last one, the next one must be within 6'; that's 12' between them.
