1- yes, each time you select "intelligent" your item gets a new ability listed underneath Intelligent, including the first time.
2- the spells being fixed/replaceable seems to be either- RAW fixed as you choose your spells, or up to your GM to decide how that will work for you.
But you get 5 "points" to allocate into spells. Each spell level costs 1 point, so a lvl1 spell is 1, a lvl2 spell is 2, etc. You cannot take a spell with a level higher than your current mythic tier.
As far as how it seems to be RAW, you choose any spell list, and once chosen that list is what it's dedicated to.
Points are only given when the ability is chosen, and do not accumulate.
3- I'm gonna be honest THIS right here is constantly racking my brain. I genuinely cannot find a single source of info on WHAT that "cost" is.
Personally, my fellow GM and I have agreed that it's simply the built in "Legendary Power" pool points you get at its creation. And then you can dip into your Mythic Power pool as usual.
But I would LOVE an actual response with an explanation on this.
