Thanks a lot for the help, Selden. I think I had a look on existing stars, but I may have done badly/modified a few things.
I had the numeric values, but I didn't remember what it indicates...

Would those could be possible then? (It's what I have in my STC file)
Surya K3 III
Nayir O5 V (with -4.2 in absolute magnitude)
Mundilfoeri A0 V
Sòla D0 A
Hyperion G2 V

When used as part of a number, "billion" is normally used in the singular, without the "s" plural suffix.
Thanks, I may have done the mistake on the stellar systems maps (but I thought about it then). For this one, I just forgot and used my french habits .

I assume the background picture shows part of a real nebula. Which one is it?
It's the Carina Nebula. I used a zoomed part for the stellar system maps.