Thanks! They're going to have decorative boarders and the constellation titles in latin and english at the bottom in hand drawn text. I've been toying with the idea of putting a background on them too, but I'm not sure if it'll become too busy.
If you keep the background overall simple you shouldn't have too many problems. You can use more muted colors probably or even have the background slightly transparent on top of a simple color after you finish. You could even use the color you already have laid in this piece to accomplish that maybe. Then you can make a pretty decently detailed border to frame everything well together.
I sort of gave up on the tarot card idea. I just couldn't seem to get it to look the way I wanted it to... Then I had a brainwave and have re-done them in a very simple graphic way. Well I'm re-doing them, I've not finished them all yet!