score:7
I did this exact connection yesterday, so...
Once you clear immigration/customs in terminal B you will immediately come to the baggage re-check area. Presuming that your bags are already tagged all the way to LAS then you will simply need to drop them at the re-check area. If your bags are not already tagged then there are counters available where they will be able to check you in for your next flight and tag your bags.
Once you've dropped your bags, the preferred route is to then to head to the (free) AirTrain which will take you to Terminal C where you can pass through security and go to your gate. It is also possible to clear security in terminal B and then catch the air-side bus to terminal C but this will most likely be slower and more complex to work out the route.