A5/2 session key derivation
The authors state in 4.3 that the design of the cipher has the following clever feature:


  The dependencies between the LFSRs and the keystream vary greatly with the initial value of $R_4$ and since the variables of $R_4$ play no role in the value of the keystream, so it is not possible to find them.


So, later on they suggest the values of $R_4$ must be bruteforced, as a precomputation.

As for your question 2, you need to plug things in, as in the equations at the end of section  4.3.