Torsten, my thoughts:
1- aligns in Align mode, then you switch it to Nav. However, you can simply switch straight to Nav, and it will run through its align mode then automatically engage Nav
2- Aircraft equipped with GPS can use GPS/GPS for position fixing, which is very accurate-I thought all B737 700-900 had this. The next most accurate mode is DME/DME. Then VOR/DME although this is not very accurate.
3- not sure. I think it will still give a wind vector, although it may be inaccurate.