We did this once a few years ago. I have to say my favourite part was creating a sensory wall – (just google it and you will be inspired with lots of different ideas).
Also we made sure to have a space which could work for different needs (parents/EP/ SLT etc) I guess it depends on how much space you have. We got a tent to create a darker space within the room as well as harping on about adjustable lighting.
Furniture we chose height adjustable and standing desks. A IWB that moved up and down the wall. Ikea was our friend.
I suggest that you make a list of all the things you would like to see in the classroom. Print out pictures and go from there.
Good luck and enjoy.