Does it matter if you put a 1 star vs a 10 star card to the grimoire?
It does (Unless it got change) , not sure by how much after they buff sorc/necro. You can probably find the info somewhere.
It increase the stats of the summons, along with the skill level.
It also seem to affect critical hits occurrence, but slightly (need confirmation).
Defense and offense also increase along with SPR and skill level.
but even at 1 star it already isnt so bad. is it worth it getting the 10 star one? how better is it?
Each star gives your summon 5% more stats (including attack and defense) iirc. A 10 star summon should be 50% stronger than a 1 star one.
So for maximum godlikeness do I need to have both 10* for primary and secondary cards?
More like for maximum relevance.
I’m not sure but morphed summons should supposedly have the same stats as your primary card, but It seems that here in iToS, it’s currently not functioning.
My advice is just try to get your primary summon to level 10 for its max potential, considering also that some cards are incredibly cheap for it to be maxed. You’ll probably only use secondary when your pirmary skills are on cd so its up to you if you want to level up your secondary.
If both primary and secondary cards are the same type of boss, then no you don’t need to have a 10 star for both.
If they are different, and you want to morph them for utility or w/e, it’s recommended to have both be 10 star so you can use either one as primary.