The staff will go over what to pack. Generally kids will need a change of clothes in case of accidents, a hat for outdoor play and enough nappies for the day if your child is not toilet trained. Sunscreen is usually applied by parents prior to the day (staff don't have time to do all the kids). Clothing needs to be practical for messy play, and easy for kids to manage independently if possible.
Most preschools have a rest period after lunch, even if not all the kids sleep. If your child uses a blanket, soft toy or some other comforter you can pack that, and a sheet for the mattress. They usually just supply mats, the parents provide the bedding.
They may ask you to send a water bottle with your child's name on. If you are sending food, containers need to be labelled as well. The preschool will give you information about what food to send. If they have kids with allergies, they may ask for certain foods not to be sent at all (in case kids share).
As for how long you stay, the staff will probably be quite flexible and allow you to work out what suits you and your child. Some children become distressed when Mum goes but then quickly settle, others don't cope with the separation and remain miserable. You can ask staff to contact you if your child is unhappy, and you can also ring in to check whenever you like. They will probably be quite happy for you to have a few sessions together with you child if that makes it easier.
As for a routine, I don't think you need to worry to much about that. The preschool environment is so different - with all the kids and activities on offer, it won't feel anything like home to your DS so anything you establish beforehand will probably be forgotten anyway. Most of the centres have free play first, while kids are arriving and settling in. They will have a range of activities set out and kids pick what they want to do. There will be art or craft tables, dress up corners, blocks or cars out on the floor and other similar choices. Midmorning they usually sit together for 20 minutes or so for a story, some songs and other planned group activities. They then have morning tea and more play (often outdoors). After lunch it is rest time, then maybe another organised group activity followed by free play until home time. Different centres will vary a bit, but it is never structured all day long like school.
I think it is important for you to appear happy and positive about the whole deal, even though you may feel quite anxious.
If your ds picks up on your anxiety it will make him scared.
Talk to him about all the friends he will make and how much fun he will have. Hopefully that is exactly how it will work out!