I agree a statement is definitely a must! DS2's school is brilliant about supporting him, and even they insisted we get a statement for him. Not only does is set out what he needs, but it means that support on it must be provided. Our senco stated that the statement is also helpful for the school, because if higher ups (LEA I suppose) try to get the school to cut back his support for this or that, the school has the statement in place and can say "no, he is required to have this!"
Something to consider may be any visual aids prepared in the next month or so in order to allow him time to familiarise with them and possibly use them at home in order to make the transition to school easier (something familiar in the classroom). It's a good idea to make sure there are Makaton trained staff available.
Also I would suggest that you meet all the people that are working with him (staff and support), and meet with any that are doing any type of programmes with him (speech therapy, fizzy, etc) on a regular basis for updates and to find out what they will be working on with him just a bit ahead of time. We found that by doing this, these people seem to be much better about keeping us informed, and it allows us the opportunity to mirror some of the information at home as well. Home/school communication book is good thing to have to keep them aware of upcoming appointments, ongoing issues, as well as them jotting notes for you about progress and problems.
If he is on an IEP (which he should be), make sure there are regular reviews (ours are every 2 months), and that you attend each one if possible. Initially, school personnel at the IEP reviews were more "discussing in front of me" during the reviews, but now they actively discuss the information WITH me in the reviews as well as asking my opinion and what things I would like focus on as well.
We asked and received email addresses for those that come to the school to work with DS2 (senco, the ATS worker, the preschool worker, speech and language therapist) and requested that they email us prior to visiting DS2 at the school. He often has appointments that take him out of school, and this way if they are planning a visit when he may be gone due to an appointment, we can email them back and let them know. It has saved us hassles on a number of occasions. It also means we have an easy way to communicate with them to catch up with how he is doing or allow them to let us know things they'd like us to help him with at home. Also, I'd say 90% of the time, when they're popping in to visit DS2 at the school, they'll say in their email "if you'd like to meet at that time to discuss how he's doing, I'd be happy to meet with you"...to which I of course reply yes! We've also emailed the senco regularly to let her know where we're at with appointments and progress on various bits of paperwork that need to be organised. It's soooo much easier than trying to catch them on the phone, and it gives you everything in writing that you can print off and keep records of.
Because your son has epilepsy, I would make sure that they have a specific plan in place in case of a seizure. Is staff trained to recognise and deal appropriately with a seizure? Will students be given a very brief discussion that he has a medical problem and if he appears to be ill, they should let a teacher know right away (always helpful, especially on playground)? How do they handle notification to you of a seizure - at what level would they call paramedics to respond? This is something that definitely needs to be sorted prior to him attending, so that you know what their plan is and are comfortable that it is being handled sensibly and safely.
And always get copies of EVERYTHING!!!! (and let them know you want copies of everything! 
)