Use all three if possible. However, don't be scared to use only one or two of them. When I use prop nuts (safety nuts) on my four strokes, I use only the safety nut. Some will say put the original nut on, then tighten the prop nut up against it. I dont' do this, as it looks hideous. I simply put the prop on, slide the washer up against it, and install the prop nut (safety nut) as tight as humanly possible. I've not had one come off yet (knock, knock, knock). I have, however, had a four stroke blow up a plastic spinner, so I don't use those anymore on my big four strokes.

Case in point. I was setting up my saito 100 the other day on my P-51. There wasn't enough room to install the regular nut and the spinner adapter because of prop hub thickness. I would have just installed the adapter by itself, but it wouldn't go all the way. So, I installed the saito locking nut (your "number two nut) on backwards--with the locking mechanism facing outward, and the flat part of the nut up against the washer. Then, I screwed the adapter down to the lock nut, and it locked it all together perfectly. So, there are several ways to "skin this cat." How you have done it is just fine. If you ever get into a situation where only two, or one nut will fit, then go with it. Just make sure that those two (or one) nuts are tight, as tight as you can get them with a 6 inch wrench. Not some wimpy prop four way, but a regular 6 inch wrench! Do that, and you'll be fine!