John, both sets will be very flexible and are designed to allow people to use their existing collections. The default for these rules are a scale of 1:20, but they will work at 1:30 or 1:40 (the later may require modification of movement and firing ranges, but this is covered in the books).
1:20 may produce units larger than some gamers are comfortable with for some battles, particularly early in the conflicts. At 1:40, full strength battalions for the Crimean would be around 24 models, but many of the smaller infantry units would only be around 10-12 models which would be quite brittle in the game. There are guidelines for brigading these understrength formations to form 20-40 model units.
Actual basing is left up to the player, but the guidelines in R2E still hold. Units may be based in any manner you like, but multi-model stands of four, six, or even eight models are recommended.
Barry may have more to add...