Also on the topic of the star creation itself:
While there might not be the stars you desire in the simulation, you can easily create them yourself. Just choose the according mass, radius, temperature and luminosity.
If you want large masses or radii, you might need to turn off Realistic in the stars Basic property window or it's gonna explode.
The luminosity doesn't really change the look of the star, because it's hard to replicate starring into the sun with a silly old LED screen. (Also no one would like to play, if they were constantly blinded)
But, if your star is more luminous it might burn up close planets or simply make them hotter.
The most important part however is the temperature, because that defines the colour of the star.
Just look up the corresponding colour on Wikipedia or try experimenting yourself.
You'll also notice, that in game the colour won't change, once you're over 30000 K, as you can also see in the diagramm in my last post.
Those stars are also dark blue, like they should be.
As for brown dwarves, just take Jupiter and increase it's mass. Around 50 Jupiters, you should see an effect