> Do whatever you want for distances between stars

Actually, this is very problematic as well. As it stands, astronomical distances are quoted in single/thousands/millions/billions of kilometres, astronomical units (Earth-Sun distance), parsecs and kilo- and mega-, and then light-years (and thousands, millions, billions).

I would strongly prefer to use metric units: metre, kilometre, megametre, gigametre, terametre (AU is around here), petametre (parsec and light-year is around here), exametre (about a thousand light-years), zettametre (about a million light-years), yottametre (about a billion light-years). The scale ends there because the observable universe is about 886 Ym in diameter.