Well things are not set in stone, because we are working with licensed technology from Visage Technologies, and right now that activates per machine and not per user.
We want to work to get it to be in line with the Steam philosophy, of having it work per user, and not per machine between machines of the same platform , but I cannot say whether or not we will succeed at this point.
So far assume that a license will be needed per machine , and migrating from one machine from another on the same platform (windows to windows) may not be impossible, but it will be probably a complicated process.
Licenses for different platforms (Windows and Android) are different even for development, so you guessed right, those will be different for distribution for sure.
Official avatar packs will be tied to the license that you buy them for. Pricing scheme for them will have to be decided so that producing them will be sustainable, so it is a bit too early to make promises about exact sums right now . You can deduce our initial intended prices by looking at the Difference between Explorer and Grand explorer.