Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
Irelia is, from my point of view a hybrid. The playstyle is very much up to the player.
I have only picked 4 items because u will rarely get more cash than this. If u need more go for either a zhonya's ring, if the ennemy team has alot of armor or a Madred's bloodrazor if they got health. For magic pen get a Void staff.
Summoner spells I would always pick Flash, but the other spell could be swiched out for either: Clarity for more mana (this should not be needed) or ignite, just to get that last bar of Hp.