Military P38s are dated from a 3 letter code, and not a serial number.
5000$
You will need to contact Walther to find out.
Yes.
1961
Try posting at p38forum.com
http://www.p38forum.com/
Dieter Marschall's book on Walther has sn data in it.
Try asking on the p38forum.com
Try the P38forum
100-1000 USD or so
The Walther P38 with a serial number 6660 was likely made in 1940. The P38 was produced during World War II, and early production years can be identified through their serial numbers. However, for precise dating, additional information such as the manufacturing code and proof marks would be useful.
Someone at the P38forum.com should be able to help