For the short id if we create one from dev server and then imported the same on production does it going to change?
The import doesn't change the shortid.
secondly, what is the exact difference between dev env and prod env?
The server is considered as production if it is used by users outside of the dev team. This means that the continuous integration server is considered as development for example. However UAT server can be considered as production if it is reached by the users outside of the dev team.
lastly, how many dev servers we can have?
You can have as many dev servers as you like and you can use the same license key on the dev servers.