Here’s the strategy I’ve used during my gameplay. It’s a slow strategy, but it has worked for me.
Any time I get a brand new creature, I hatched that ASAP. Beyond that, I started with the cheapest creature and hatched enough to have a level 40 (8 creatures) or 2 level 40s if it had a hybrid and worked my way up from there. The first hatchery was for Commons, Rares, and Super-rares, as well as any VIPs I came across. The other three hatcheries are for Legendaries. After 18 months or so, I’m now working on leveling up my tournament creatures. So, it’s a slow process. But one that has helped keep me out of trouble.
Once I got to the point were I had completed at least one level 40 creature of everything that hatched in one day or less, I used the first hatchery to build up multiple copies of Common, Rare, and Super-rare hybrids.