E6000 is the tried-and-true glue.
As far as I know (not very far) the TIE helmet has four screws; two on each of the side parts connecting them to the faceplate. One is in the upper corner next to the mohawk, the other is down by the ear piece (and sometimes covered by it (?)).
Are you planning on joining the 501st? If so I'd start by doing some research on your kit to find out how accurate it is. I don't mean to be negative, but 501st suppliers generally don't use Ebay and a lot of the stuff sold there isn't up to 501st standards (sometimes even if the seller claims it is). That usually doesn't mean it can't be approved, but it might require some work.
A good place to do this research and/or learn how to build your kit is the Jolly Roger Squadron forum. JRS is the TIE pilot detachment and home to most things TIE in the legion. http://www.jrs501st.com/forums