Roedy Green wrote:
In a 75 light year radius sphere centered on earth have you an
estimate how many stars and planets there are, or could you give me
density numbers I could use to compute that?

There are about 50 known stars within 16 light years:

http://www.cosmobrain.com/cosmobrain/res/nearstar.html

So that equates to a density of about 2.9 x 10^-3 stars
per cubic lightyear. For a radius of 75 light years that
translates to about 5,000 stars.

As to the number of planets, you'll have to dig up an estimate
(or make a guess) as to the fraction of stars that have
planets.