A fleet command ship, like the Caldari Vulture, can use 3 gang links at once. I understand that you can't use 2 of the same gang links at the same time.
My question is how do the ship bonuses, module bonuses and leadership bonuses stack? Do they stack or is just one thing selected by the game mechanics?
For example, if I had Siege Warefare 5, Siege Warfare Specialist 5, Leadership 5, and Commandships 5, what kind of bonuses would I be giving?
Lastly, if I were the fleet booster and there were 2 squads with legal squad leaders, both with leadership five, how would that affect the boost given to the squad members?

Thanks for all the great replies. It’s pretty complicated stuff and I appreciate the help.