About the summoning skill. Do you have to declare which unit you will summon in your list? Or you can just pick, for example, 200 points pool and summon what you want?
I think that depends on the tournament. But normally the unit you summon is not declared before the game. Your opponent will probably still know, based on the number of points or the models on the table. Or they will see the miniatures in your case.
Yep, you don't have to tell it before. You just have a reserve pool of "nameless" points, you declare what you're trying to summon only at the moment of casting.
how does this work with the "Engine of the Gods" of you roll 14-17 you can set up an unit on the battle field. Do you also need points in your reserve pool for this unit?