How to calculate how much paint to buy?

[SPP]

I got the following dimensions for the area I need to paint: 

1) Ceiling Area: 50 sqm 
2) Wall Area: 68 sqm

The ceiling is plasterboard, the walls are VJ. 

I have attached photos of what paint I am using for walls and ceiling. How do I calculate how much paint I need and how much this will cost? 

Ceiling Plan: 
1) One Coat of Primer
2) One or Two coats of Ceiling Whit

Walls: 
1) Two coats of wall paint (VJ is already primed!) 




Also, been preparing the VJ by sandpapering places where I had to use Gap Filler. See below. Some of the bare wood is exposed. Do I need to go over this with Primer? 

[SPP]

Thanks.