Consider just buying the OEM one. All of these aftermarket ones with their X or Y times greater strength are fine, but given you should be replacing the belt after the next 100,000KM I am not sure its worth it.
I assume those a different types of gear oil for the box and diffs? Also think about the transfer case.
Think about just running some coppers. Yes you have to change them more often, but for $2 per spark plug, who cares?
I have never heard good things about flushing products. Your milage may vary. IMHO you are better off buying an extra 2L of engine oil, half drop the oil, top up and run it through, then drop the lot and refill.
As per above. Consider completely removing the radiator and having it professionally flushed. I posted up a tutorial for that awhile ago.
As others said, get something better. Motul DOT5.1 seems quite popular.
Lucien.