Just got my sixth aegislash
44 more to go>>23349621If you don't plan on buying diamonds, then I recommend you to save them.
If it's a non-fever kyogre then there's a high chance it'll stay for a while even if you don't land on it.
As for stars, I believe they're completely random. But I've noticed that if you're missing a single pokemon in a balloon, it will appear on it after you catch the rest.