Cutting the sound hole out is probably the trickiest thing to do accurately if you don't have a circle cutter, but it can be done with scissors if you are careful and the pattern of the rosette tends to obscure any slight variation.
The problem I found was sourcing the film he is using - that type of double protected pre-glued film - in that size sheet ?
I'd like to do one guitar with a golpe - as then it can be the 'have a play' guitar when nephews come visiting !
Are not the Herco ones pre-cut?
I recently bought two golpeadores from the Felipe Conde shop on line for a small sum and cut the sound hole with a craft circle cutter.
It is important to make sure there are no hairs or other debris on the top and to avoid trapping air bubbles. You get one chance to get it right.
Thanks - found the Conde items ( little imformation on site - except size ! ) but good price.
Also - musicaladn.com in spain ( en ) have a variety of sizes - inc the electroctic Ortola types. Full size transparent stick on for 5 euro - post UK 6 euro ( 200 x 200 )
I feel on a domed top it maybe is best to lay two halves - with a narrow gap middle ? You only know its not laying flat until its too late !