Yep, that's how it works. You'll get 6 Omega Crowns for the craft, and then it looks like you'll have 12 total. It takes 15 Omega Crowns to craft the dragon, so you'll need three more.
After the you craft the 6 Omega Crowns, an 'Ask' button will appear on the one of the lesser crowns (I can't ever keep the names straight- wish they were three different items instead of three different types of crowns, lol! I think it's the plain one?) When the Ask button appears, tap it and your Neighbors list will pop up. You can use that to ask friends to send you one of those lesser crowns. Every little bit helps!
The two lesser crowns are collected through harvesting food and breeding/hatching, IIRC. I usually just play as normal and then check Spell Shop every once in a while to see what my crown totals are. Just keep on trucking and you'll collect enough to craft those last few Omega Crowns.
And yikes is right! I totally forgot how expensive the Black habitats are. If you craft Gentleman, you won't need the Night Dragon to breed him. Crafting is much, much easier than trying to breed these event "commons" (who aren't so common, as you can see by all the frustrated posts in this thread).
What some players do is sell Night eggs right off the nest until they have collected enough coins to build the habitat. That way your game isn't left at a standstill with an unplaceable dragon egg blocking the nest for days or weeks on end. But, if you are close to the 500,000 coins needed for the small habitat, I'd say keep going. Black is a fun color and there are many cool black hybrids that can be bred.
Addition: Another consideration re: purchasing the habitat now is having enough coins leftover so that food production isn't interrupted. That is important in your particular situation, during this event, since you need to keep harvesting food (and hatching dragon eggs) to keep earning those lesser crowns.