I am so sorry for the loss of your mare. If I didn't live several states away, I would be more than willing to give you a hand. As for bedding, shavings on the bottom to "sponge" up any urine, with hay on top should be okay. In my opinion, do not use the pelletized bedding. I had a horrific experience ( a few years back) with a young filly digging for the pieces that were intact, and she impacted, sad story, but babies will put anything in their mouths.
I don't think I would allow free choice of the milk replacer, unless you are in a bind and need to run out for a bit. I am only saying this because you don't know how long it will sit before it is consumed. Make sure you clean the dish well between feedings, to prevent bacteria from forming.
If you are going to start feeding a bit of mare and foal you can saturate it with water and make it into a very wet mush. I would be more concerned with getting the milk replacer into her rather than large amounts of feed, the feed will be a bit harsher on her digestive track. I am sure her sytem is stressed enough right now with losing her momma. And as much as you want to make certain you don't give her too much, probiotics are a great thing to keep those healthy microbes in her GI track at a good level. I am sure if you give your vet a buzz, they will be able to give you some tips.
Keep us posted
Carolyn