It needs a neutron source to start fission, but once it's going, in theory it can self-sustain as Th decay genearates radio-isotopes. Furthermore it can breed fissile fuel with thermal neutrons, which is generally seen as an advantage.

The neutron economy, however, is very slim. Several of the intermediate decay products are neutron absorbers. This is why you see a lot of proposed liquid thorium reactors, there are various proposals to use chemical reactions to remove neutron absorbers from the fuel while the reactor is running (something that would be challenging with a solid reactor).

You are correct.

You start with thorium plus a fissionable isotope of uranium or plutonium. The fission neutrons convert the thorium to U-233, which is fissionable. After that you rely on U-233 fission for neutrons and keep feeding thorium to it.

It can be done with solid fuel but with liquid fuel it works out really nicely. You can fission pretty much everything and have just fission products left over, which means a lot less nuclear waste that only has to be contained for a few hundred years. And you're not shipping anything fissionable to or from the reactor.