That's pretty neat.

To answer your question. The guy in the first vid used two 5ohm resistors in parallel, which equals 2 1/2 ohms. So you could just get one 2 ohm 10 Watt resistor.

Now don't take this next part the wrong way. I'm just concerned for your safety, I don't think you understand how dangerous it is to mess around with electricity without the proper education/ training. Watching a youtube video doesn't make you an expert.

The switches, connectors, L.E.D.s, heat shrink tubing, and pc board needed to make the supply into a desktop supply would cost well over $14. Not to mention all the tools.

It makes more sense to me to have a permanent supply for the spray both. Something you could just plug in when it's needed.

Going through all the trouble to make your own cheap desktop supply makes sense if your going to be using it a lot with different projects, i.e. prototyping, testing circuits, etc. 

That's just my opinion, and you seem to have already made up your mind. So good luck to you and don't electrocute yourself please.