Hi and welcome!
If you have questions about a specific holiday, you could always ring the SWK number and talk it through with them. Or email if you prefer.
I think the holiday you are talking about says there is a train station at New Milton (which I think it on the london line) so you probably wouldn't have to change. Just make sure the train you book stops there!
Foodwise - you will be limited with how much you bring if you are not travelling by car. There should be a shop onsite (but wont be cheap).
When you arrive, you will be given your lodge/villa number and directed to your accommodation. Accommodation is usually shared so, others will meet you there.
From memory, I think the SWK coordinators mobile number will be on your email. But if you take the number of the reception of the place you are going to, you can always call them.
Hope this helps. Be brave, it will open up a whole new world