Excuse me, the servo I use is not available any more.
Important is the distance between the upper side of the mount and the centerline of the steering rod. It must be 12,5 mm, otherwise the steering rod will not fit properly through the provided hole.
I think this one should fit: http://www.hobbyking.com/hobbyking/store/__27725__Turnigy_8482_TGY_R5180MG_180_Degree_MG_Analog_Servo_2_0kg_0_12sec_12g.html
40A for a regulator is amply even for the motor boat version, though you will have much reserve for other things but 30A is enough.
If you use the airboat version: 20A suffices.
5000mAh are by far to much! With this weight you will probably get a submarine ;-)
1000 mAh will be enough, I use 850mA but it last not for long.
The receiver is ok, I have the same one.