GFCI's are not for overload protection, that's the circuit breakers function. GFCI's monitor the current in the hot and neutral wires and will trip if the difference is between 4 and 6mA to protect the user from electrocution. I'm assuming that the circuits are 20 amp with 12 gauge wire, you shouldn't use 20 receptacles on 15 amp circuits. If you're going to install a GFCI on a circuit with another GFCI downstream, use pigtails to the Line side, and do not use the Load side. Also, check the old receptacle to verify that it's not already GFCI protected from an upstream device or a GFCI breaker. Those receptacles should be labeled "GFCI protected outlet" in those cases, but it's not always done.

Always a good idea to install a GFCI no matter where and closest to the breaker as well as those wet areas. One thing you didn't mention is that you need to install the correct amp version. A 20 amp only on a 20 amp service (12AWG wiring/20 amp breaker and a 15 on a 15 amp service, (14 AWG wiring/15 amp breaker). Also a GFCI protects all receptacles downstream of that device.