No you can download apps without jailbreak, but you will be able to download apps that have been disapproved by apple if you have jailbreak.
No
Yes, but downloaded apps from Installous will not sync with iTunes.
You do not Jailbreak iTunes; you jailbreak iPods and iPhones.
No, use redsn0w.
If they are apps downloaded from cydia, then no, because cydia apps don't sync with iTunes.
You can without but the easiest generally do use iTunes.
no, you don't need an account.
If the movie is being downloaded to iTunes then you will need to have a connection either wireless (WiFi) or wired will work. Once downloaded the connection is no longer required to watch the movie.
Assuming that the movie has been downloaded from a source other than iTunes and you now wish to add it to the iTunes library you will need to check that the movie is in a format recognised by iTunes.
Not At All...... But updating your ipod will remove the jailbreak
Yes.
No
No