The ESY IEP is usually just a more focused (limited) version of what is already on the IEP. (Usually more limited only because the school day and span of the summer school are more limited.) If you want to add more than just ESY at the meeting, ask for a new IEP meeting. The school system is obliged to have them once a year, but these meetings can happen more often if anybody on the IEP team (including the parent) calls for one.

I would definitely message her again. Maybe she has a lot of kiddos to manage. It's fine to follow up if you haven't received a response.

It’s called an addendum to his current IEP. It sounds like they are recommending it. I would mention to his teacher before the day of the meeting that you would like to add accommodations to his IEP.

I messaged the case manager but she hasn’t responded? It’s been 5 days.