I've been asked about parking and such, last year we parked in the car park marked, I cannot remember the cost but it wasn't unreasonable. I've highlighted the apartments as well, though you still enter through the front door. At the apartments there is a side/fire door, handy for getting extra people in.
Sleepzone's website suggest you can checkin from 3pm onwards. they have a waiting room and bag storage if you arrive early anyway. The rooms are booked under my own name. Oh and they take a €20 cash deposit from every one (so 6 of ye).
Any questions don't hesitate to ask.