I say, if it is going to take a lot more hours of work, you've got to ask for a larger increase in pay.
Making up a deficit in skills--would that be on your own time? That doesn't sound good to me....
At the same time, if they are willing to hire you, hopefully, they'll be willing to help you grow into the position. Ask about what kind of on the job training you'll have if/when they offer you the job. If it were me, I would be clear at the beginning that you have a lot to learn, please be patient and you'll work hard (but not necessarily an absurd amount of hours).