You are aware of the Star System creation rules on p. 302 ff. of the Shackleton Campaign Setting?
If you need crunch regarding gravity etc. have a look at p. 145 ff. of the Core Rulebook. Take the gravity spans for each class, take min/max and 9 equidistant numbers in between and take 2d6 for a nice gaussian distribution.
Maybe this writeup of using the random tables of STA is of interest to you…? 