Well, for the shadow part, if ever people (and steve) ever think that it would be a usefull addition, it does not has to be coded with fully implemented physics... It could be a type of a flag and a location given to a ship telling "ok, I am hidden from the light of that sun behind the planet"
Hidding from the sensors of an other ship behind a planet is an other story which requires quite a bit of computing (I have done it for a previous programm with stars emiting solar wind, planets and and some sailing space ships). Though, maybe a Database powered software such as Aurora would be efficient at it... I have no idea...