No, i stated that he can make 1 clone, then he and the clone can make clones
that's 4 clones
and don't forget he has amaterasu... something shishui doesn't know he has and he can get it on him
He can't do that. Just using one clone leave him with 50% of his chakra. Doing a clone again after that, and he will stay with 25% of his chakra, and like you know, even with 30% of his chakra he can't even use MS technics. So it would be an error if he think this way. Also, he won't even be able to maintain the clones for too long. Kakashi said to Naruto that "the most you use clones, less the time you can maintain them" or something like that, "especially when you don't have enough chakra(talking about his case)". He said it to Naruto when Naruto asked him why he didn't use tajuu kage bunshin to train and become much more stronger this way. And like you know, chakra is one of the main problem Itachi has when he fights. Another reason why using clones like that could be a waste of chakra and could penalise him during the fight. That's why generaly he only uses one clone.
For Amaterasu, you're right that could surprise Shisui(since he lacks of feats, we don't really know what he could do), but we're not really sure Shisui doesn't know it. The way Itachi explained it to Naruto, Itachi is not the one who killed Shisui. That means Itachi maybe had already MS when Shisui was alive.