First, I'll state that for this post, if it's stable for a half billion years. I'm not worried about a million eons later. That being said, I have a couple rules of thumb in my head, that may or may not be pretty good and I'm looking for more. My first rule of thumb is if bodies are about the same size like a trinary star system, the outer orbit should be at least ten times the size of the inner. The second is, if the primary is between 100 and 1000 times the mass of the orbitals, the outer orbit should be at least twice the size of the inner. The last one is if the primary is around a million times the mass, the outer orbit shou be at least 1⅓ the size. If anyone could make these better, add more or just give me a math formula that would be awesome .