Appropriate Mass Units

I'm designing game objects that get all their motion from calls to setImpulseForce(). I basically total the net forces acting on an object, modify by the time delta to get an impulse, then pass that to setImpulseForce() with gravitic=true where mass is finally factored in. I am setting mass on the objects manually.

I haven't yet gotten to collisions, so I'm asking this question as a "heads-up": what are mass values to watch out for, i.e. what is too big and too small? It would me nice to think of 1 mass unit equal to 1kg, and adjust all my acceleration variables per entity appropriately, but obviously all these numbers are relative and in that sense it doesn't really matter. I just want to know if there are values to watch out for...

For reference, I would think of my main character as 100kg, with other objects ranging from 10-100,000kg.

This question may be too general to answer, but if anyone has thoughts I'd appreciate it...

Thanks,

- Matthew Durante