I had to mix feed from day 2. I honestly can't remember how much milk he took, my mind was a mix of how much he'd had and how much I'd expressed. I think by the time I switched to all formula it might have been around 60ml but I could be right off there! Sorry! However, I think there is a guidance amount on the carton of formula for different ages so I would start with that, if your LO drains the bottle then make more and keep a written record so you know to make more next feed, you'll know in a day how much she needs. Always make bottles so that she stops feeding when there is a little (say 30ml) left in the bottle which you discard. This way she continues to dictate how much she takes.
I would keep the times the same.
I don't know about going cold turkey because I mix fed and my situation was with problems BFing, I could only express so DS had a bottle from day 2 and didn't bat an eye whether it had breast milk or formula in it.
Hope someone else comes along with their experience for you.