Welcome to BYC!
Looks and sounds like you have a great set up. Your girls will roost when they decide it's time. You can try setting them up on the roosts when it starts getting dark to give them the idea, but don't be surprised if they jump right down the first few times. Take the cardboard boxes away and they will look for the highest place they can find to sleep.
As for placement of your nesting boxes, make sure they are lower than your roosts or the girls will sleep (and poop) in them at night. Whatever height you put your roosts and nest boxes, make sure they have a ramp up to them, or a wide board in front of the nest boxes to land on if they fly up to them. The bigger the hens, the lower I like to put the nest boxes. Bielefelders are large birds, so I wouldn't put them too high unless you have a ramp to them. When you see their combs start to get bigger and start turning red, it is time to install the nest boxes and let them get used to them before they start laying. Put a fake egg or a golf ball in the nest boxes to give them the idea of what they are for.
Cardboard under the roosts sounds messy to me, and the girls will probably tear it apart and eat it. Plus, any wet poops will invite the growth of mold or mildew in cardboard if it is not changed often. Also, cardboard easily absorbs moisture and could raise the humidity in your coop - a very bad thing. And the spaces in the corrugation can harbor bugs.
Check out this thread for a much better idea -
https://www.backyardchickens.com/t/...vert-warning-graphic-gross-poop-pictures/0_20
When introducing new foods, sprinkle a little of their grower crumbles on it. They will happily peck at the crumbles and quickly discover the goodies that lie beneath.
I don't use medicated chick feed at all, but you should check the recommended age at which to switch to non-medicated. Leaving them on medicated too long can cause a vitamin deficiency (the medication is a thiamin blocker).
You should not have to add any supplemental heat during the winter. Your girls should be all feathered out by now and are quite capable of keeping themselves warm as long as they are dry. Good ventilation is the key to winter survival. If you plan on only having the 2 girls, your coop is plenty big and looks like it has excellent ventilation as long as they are protected from any drafts and wet weather.
To tell them apart, you can use a colored ziptie as a leg band on one or both of them. Avoid red as that is a color they love to peck at. Be sure to check it often while they are growing to make sure it does not get too small and cut off the circulation in the leg. Change it as necessary. Once they are grown, check it once in a while to make sure it is not causing irritation.
Good luck and looking forward to pictures of your girls...