1) Gen 5 mons with gen 7 mechanics and learnset(ex:flygon can learn dragon dance etc). Im not sure about pve, but Volt Switch and Uturn works in pvp battles.
2) Yes. breeding 2 shinies have a 100% chance to hatch a shiny( actually you can only breed a shiny pokemon with another shiny).
4)No. Stealth Rocks is'nt an egg move, spikes is.
Breeding a pokemon with a low chance of being a female costs more than usual. The cost of choosing a pokemon's gender in daycare depends on the natural odds each pokemon has.
Ex
Rattata: 50% Male / 50% Female, costs 5k to choose from both genres.
Charmander: 87.5% Male / 12.5% Female, costs 5k to choose male, and 21k for female.