The great thing about air is that it breeds with all of them with an 8 hour rate (apart from the sandstorm, but we won't mention that **cough cough**). So optimal breeding to not double up ... You have 144 elements required, so 72 dragons is the minimum you will need to breed to have them all covered. You have 72 spots available in your HC? Like you say, let's start with half an half Mud and Quake. Quakes are better earners, but if you're just breeding them to put in the HC it doesn't really matter.
9 Quake - 6 hours
9 Mud - 6 hours
That will complete your Earth shrine and leave you with
14 Storms - 5 hours
This will finish off your Lightning shrine and leave you with
16 Snow - 8 hours
This will even up your numbers to
2 (more) snow
You can adjust these last breeding numbers when you get your Air Shrine and you know where you are, but the optimal breeding strategy (until a new multi element hybrid is released, lol) is
9 Quake - 6 hours
9 Mud - 6 hours - Earth is complete
14 Storms - 5 hours - Lightning is Complete
18 Snow - 8 hours
2 Ice/Iceberg - 8 hours - Cold is complete
20 Fog - 8 hours - Air/Water are complete
That makes 72 dragons. Hope that helps.
So, I just thought I would let you guys no first, that I have a rainbow on the way hopefully. Second, I am sorry I have been gone for over a hundred pages. I am a busy body with school. And last but certainly not least, thank you everybody for the gems you have been sending! I am actually saving now which is odd for my usual lack of patience! I hope everyone is leveling up and getting breeds and shrines done! I am almost at my first silver shrine with the plant. Just thought I would show some some love and appreciation for all of you guys' advice! Thank you guys and I will keep up for
The extended weekend! Oh and glad you are feeling better poppy! And glad I could be a part of your support group! Haha. Well as I always say, "breed on!"