In the manga he summoned all of them, but in the manga its also shown you can choose which ones you summon, that's a fact right there. Him summoning Hashirama once doesn't mean he needs to summon all of them at once every time he wants to summon one.
This explanation doesn't even make one bit of sense. Are you talking about a ranking here or a VS situation? If you are talking about a ranking, then you have no choice to exclude Hashirama from Orochimaru's power as Hashirama can't be controlled so he can't be counted toward Orochimaru's power on a ranking list. If you are talking about a VS situation, its already fact he can summon whatever Edo he wants to summon. Your "weakness" for his Edo Tensei has no bearing in a ranking situation and it can be prevented in a VS situation.
Trigger what release? He doesn't start with his Edos summoned. No one starts with their summons summoned, ever, nor do they start in their strongest modes. I don't know why Orochimaru is the exception for you but its clear that he shouldn't be. He summons his Edos first, simple as that. I don't know how hard it is to understand that.
Not even sure if serious now. Do you know how summoning works? Cause I'm pretty sure you do, and anyone who knows how summoning works shouldn't be arguing something as flawed as this.