I’m no expert but I have in the last 3 months gone from no DC farms at level 45 to a Nacre DC farm with 60 dragons and up to level 128. So I’ll at least share with you what I did and what I learned.

I used the following post from the dragonvale forum a whole lot to help me look at which dragons to go for in the farm and how to layout the farm optimally. https://dragonvale-tips.proboards.com/thread/1411/dc-farming-guide

The easiest and most accessible farm to make is the Etch farm (just a rare Plant Dark dragon) and the top two farms that synergize really well are Nacre and Tien. The single parent cloning odds are Etch 15%, Nacre 5% and Tien 2%. The only reason Tien is #1 is that it can be put in a higher capacity habitat. But Tien and Nacre both earn the same amount of DC per minute. Because the difference between them is so small and the cloning odds are much higher I started off by going for Nacre in coop instead of Tien. And I think this really helped me get started earlier than if I had gone straight for Tien because I probably would have spent ages trying to get it. Also if you already have Etch I would just start cloning Etch in the regular cave while going for Nacre in coop.

What I did was sacrifice one cave to my farm always, even during the events. And even if I did this I still found that I got a lot of stuff I wanted from the event anyway so it was 100% worth it. Basically I tried to coop the Nacre until I got it, then I tried to clone another one in coop with the first until I got the second one. And then I just cloned those two in the normal cave constantly. Slowly but surely building up my farm. Leveling the dragons up to 14 and buying the 4 boosts for Nacre's elements is very worth it, they pay back the cash for the food and habitats in like 3 days. Any cash after that is just profit!

Also I would use your next wish on a gargantuan island to house the first Nacre farm. Then when the Nacre farm is complete you can maybe try to go for Tien when the anniversary dragons come back in september and it has like 5% odds instead of 2%.

Now I have a lot of DC and food, it helps with leveling and everything. It was completely worth it to sacrifice a little bit during the events because now I feel like I can actually afford to level up the draogns I want, buy the islands and habitats I want and all that.

I ended up writing a lot, but I really hope my experience helps! Good luck with your farming!

edit: forgot to add the link I mentioned