Background questions

I've been considering the idea of setting up a 'background assumptions'
page for my NRE, discussing the assumptions I make when considering my
universe (I like the ring of that, "My Universe").  Anyway, I think I've
more or less decided to use the 'offical' FTL drive, I guess I could
call it the "hop drive" which makes a number of short hops rather than
one long jump from starsystem to starsystem (a la Traveller).  Anyway,
to limit these guys somewhat, I wanted to introduce an arbitrary fuel
requirement.  I was considering 3-4 parsecs for military ships, and
probably 2-3 parsecs for civillian ships.  This wouldn't show up as a
factor of mass in Full Thrust ship design, but would force space combat
to follow logical lines of advance, with a requirement to secure fueling
spots (any gas giant will do, as will an inhabitated planet with
hydrogen refining equipment).  Just a playability issue.  But anyway,
what I was asking the Star Gurus on the list is, Is that enough
distance?  I mean, if I say "2 parsecs for civillian ships" will I be
cutting off a lot of stars from commerce?  Do I need three?  Or even
four?

John M. Atkinson