I have used Easyjet for various flights around Europe and always found them to be OK.
You book a ticket and then add luggage and add a seat which will give you the final price. obviously you don't need to add luggage or a seat, just carry hand luggage (make sure you are in the size limits or it can be very costly) and have a seat allocated when you check in.
I can't help regarding the question of wheel chairs but I have seen wheel chair passengers on the same flights as me.
Have a look at
http://support.easyjet.com/faq/en/request.do?view()=c%7B3c9e5250-ced9-11e2-ef6e-000000000000%7D
Dave