When do I have to change the differential and transmission fluids?
 

As well as the brake fluids?(Is there clutch fluids too?)

I own 04 M/T....is about to reach 50,000 miles and I am kinda worried about
because I bought this car at 37,000 miles and I have no idea what the previous owner have done...

I have done some research and found that diff/trans fluids need to be changed at every 4 years of 70,000km...I just want to make sure...

Get some Redline MT-90 (GL-4) for the tranny and some 75w-90 (GL-5) for the diff after you spent some money on replacing your coils and plugs.