Next important thing is transistor. It is used as a switch, if you can't find BUZ12 you can use similar (HRF3205). Don't use external diodes or filters on L3 or transistor because is damping oscillations and you won't get transfer more than 20%. So don't be greed and try to light bulb of 100W because you'll burn transistor very fast... It is recommended to mount mosfet on aluminum cooler.
     Coils must be made as you see them on photos ! ! ! L3 & L4 must be flat and L1 & L2 must have length. If L3 & L4 are not flat, than you tend to make classical transformer system it means that magnetic coupling is strong and you'll just waste energy radiating in radio waves and you won't get transmission more then 15-20%. And if you make L2 flat then you will get nothing ! ! ! So, it is obvious that geometry of coils is very important.