Stars are really complicated, it's not just about the mass, the age of the star is really important as well. A star with the same mass and a different age, will be vastly different in radius, luminosity, and may have even of collapsed.
http://en.wikipedia.org/wiki/Stellar_evolutionIdeally we'll simulate the metallicity and other factors at some point, but as it stands this is largely a function of the age.
http://en.wikipedia.org/wiki/MetallicityThey don't really respond in a way that is readily apparent. If you like, you can uncheck the "realistic" option and have more control over a star.
You may also want to pause the game while editing, otherwise it will update the star while you're in the middle of editing, which may cause it to destabilize, collapse, or super nova.
Also, we have most stars in our database, so if there's a particular one you're looking for, chances are, we already have it.
When you search for a star, make sure you press enter in the search window, so it will perform a full search of the catalog.
Also, stars will often be listed by ID instead of the common name. For instance searching for the star pollux, will be listed as HD 62509.
Wikipedia or astronomy databases will give you the designations for the stars. In the case of the star listed below, it's under "Other Designations"
http://en.wikipedia.org/wiki/Pollux_%28star%29Hopefully this answers your questions, if there's anything else I can do to help, just let me know.