The wilton large 1/2 ball pan serves 24 (I'm pretty sure)
Definitely use airbrush for the red & black.
Red & black icing = ick 
I did a lady bug cake, it's in fondant with gumpaste ladybugs, but you could do the same sort of idea with piped red balls of BC for the ladybugs...and if you do black icing, start with chocolate BC.
You can see the cake at http://www.cakecentral.com/cake-photo_1741845.html
Ive also done a ladybug cake. It was buttercream for the cake itself, and then a rice krispie treat ladybug covered in fondant on top. Im sure you could do something similiar using 1/2 ball pan for the ladybug and covering him in b/c. There is a picture of mine in my photos- first one. Good luck!
Here's my version. Don't let them scare you. I used mmf and I am very new to it.
For using butter cream, why not pipe red ovals/dots, and finish dressing them with smaller black buttercream dots/
Good Luck!
http://cakecentral.com/modules.php?name=gallery&file=displayimage&pid=1753042&sub=1753044
Wilton makes cans of spray color, but velcrostiletto's pink one is CUTE!
That solves the icky taste issue because then there is no red and not too much black.
Use Americolor gels to color your BC and you won't need to use the spray. I've done quite a few cakes frosted in bright red, and never tasted the coloring. Black is a challenge but starting with a dark chocolate does help a lot. And actually, if you look at real ladybugs, often they're sort of dark blackish-brown on orangy-red. 
You can just use melted dark chocolate or ganache for the black parts if you want, without even coloring it.
Quote by @%username% on %date%
%body%