I agree with the enchanting bit. Even just a single star, if you are short on gold/mats can be very helpful. I usually take mine to 4* since the fifth is so expensive.
As for runes, they are definitely a big boon as well. Do you use any of the dragons in other modes (FP, Coli, GW)? I think those should be runed first.
Without knowing that, I'd say Cutie, Spikey, Kaiju, Dracul, and Hydra are worth focusing on over Snap, Storm and Rabid. Snap's orange skill does make it easier but you probably won't use him elsewhere and once you get your heroes runed it shouldn't matter too much.
Here's what I recommend doing for each hero:
Cutie: tank set (Tree, Mist, Rock). Majors should have defensive stats on them, minors there are a ton of options. You might also want to swap one of the defensive sets for blood if you don't have any minors with lifesteal as the primary stat. If you use blood, you don't need minors with lifesteal
Spikey: Ocean with either Tree/Blood as the secondary set. You want Skill Power on your majors and looking for stuff like Armor Pen, Crit rating/bonus crit, lifesteal, CDR on minors. If you use Blood, don't use a minor with lifesteal primary.
Kaiju: Ocean + Tree. Skill Power for majors, SE/fury/magic pen for minors. Lifesteal doesn't benefit him
Dracul: Ocean + Tree. Skill power for majors, magic pen, crit rating, bonus crit for minors. Lifesteal doesn't benefit him
Hydra: You could go 3 ways here (tank, ocean or flame). I'd probably recommend Ocean/Blood at this point? Skill power or defensive majors, minors are arpen, fury, conservation, crit/bonus crit, tenacity or lifesteal if you don't go blood.
Runing seriously makes all the difference in the world.