Regarding your third point, you have to remember that Teal'c is a jaffa. He is host to a Goa'uld symbiot. If you remember, a Goa'uld can take control of its hosts body. Perhaps, in the case of Teal'c, the sarcoughagus didn't take control of teal'c's mind but instead took that of its symbiot, which then took control of teal'c.

I havnt seen this episode so it's just speculation.