The main thing you need to know is that you should assume that the IEP is not going to be followed. Stay on top of things and don't be afraid to advocate forcefully.
Second, it's bullshit that first grade is too early to be diagnosed with dyslexia. But for purposes of an IEP, all disabilities have to be coded into one of the categories listed in the IDEA; dyslexia would fall under specific learning disability. Dyslexia (which isn't in DSM V) basically means "specific learning disability in reading."
Third, the law requires that he be given an evidence-based reading instruction, implemented with fidelity. That means that have to show you that the reading intervention they are using has research behind it showing that it's effective for kids with specific learning disabilities in reading. It then needs to be implemented with fidelity -- so if the research shows that it's effective when kids get 1 hour a day, your son needs to get one hour a day. Programs should be gorton-gillingham based.