No. You may make optional contributions to other savings plans; however, the 3% employee contribution is mandatory for the FRS.
In the Investment Plan, you can only purchase military service under the second bullet below. Under the Pension Plan, you can purchase military service under three different sections of law.
Yes, funds from tax qualified plans (457b, 401a, 401k, 403b, 408a, and 408b) may be used to pay any shortfall in your buyback cost to join the Pension Plan.
The law states that rollovers from the Pension Plan must be paid directly to the custodian of an eligible retirement plan as defined in Section 402(c)(8)(B) of the Internal Revenue Code (IRC). An eligible retirement plan includes the following plans: