Is Jinshanling likely to be jam packed with hikers/tourists this Labour Day holiday?

Pamela, it won't be as crowded as Badaling section. But If I were you, I wouldn't go there during any public holiday. You know, everything becomes more expensive during the holidays, especially the accommodation. If you plan to enjoy the wall on your own, I think you should avoiding visiting the wall at weekends or during any public holiday. It's good to go there on weekdays. You won't expect many tourists.

is there toilets and how far apart

Pamela, there is no toilet on the wall. You'd better use the toilet near the ticket office before you climb.