FAR is basically a slightly buffed star with less ammo per mag.
The only differences between the two are:
TTK- (.75 for star vs .70 for FAR) this is due to the difference in fire interval (.15 for the STAR vs .12 for the FAR)
reload time- (2.80 for the STAR vs 2.20 for the FAR)
shot modifier cap- (1.35 for the STAR vs 1.45 for the FAR)
magazine capacity- (32 for the STAR vs 24 for the FAR)
marksman modifier- (.50 for the STAR vs .45 for the FAR)
As far as how to mod the FAR this is going to be mostly up to personal preference. Like the STAR the gun performs well without any mods. I personally run HS3 and Mob Sling only on mine, as for me red mods are more trouble than they are worth. Though I know players who use everything from Reflex sight with cooling jacket to hunting sight with improved rifling. You've really got to put in the time to see what works for you, its not a one size fits all weapon.
People will talk a lot about how "the FAR will never beat the n-tec" but as any half way decent player will tell you, winning in APB is more about positioning and prediction than anything. If you are constantly engaging in fair fights where gun stats are solely determining the outcome, you are not playing the game correctly. Play smart, and the FAR can compete with anything.