Yep, on the whole motherboard (under all the heatsinks locations). It not complicated at all. Proceed exactly as you would for taking off old thermal and add new one from the CPU. It's just on a bigger surface. The whole heatsink is attached with screws, so you'll need a screwdriver to take it off. There will be thermal pads on the mosfets. You can choose to keep them, or apply thermal paste on them (you'll get better temp that way, but be sure to pure it only on the mosfet, so as not to cause a short-circuit). Then you'll have to take off the old thermal paste that is on the NB and SB (on the mobo AND the heatsink) with either isopropyl alcohol or acetone (you put some on a q-tip, then rub it). Then all you have to do is apply the thermal paste on the NB and SB.
For the mosfets, I'd recommend doing the same procedure even if there was no thermal paste on them (it was a thermal pad). That way, you can be sure they are very clean.
As for the quantity, it's the same as on a CPU...not a lot ! Just enough to cover the metal, that's all.
You can look here to see how it should look like once everything is cleaned up, and the new thermal paste is ready to be applied:
Search for "what’s residing under that heat sink" it will get you at the right place.
http://www.overclockers.com/asus-crosshair-iv-formula-review/
If you have any other question, I'm here !