Gouache is amazing! My only real advice would be to use A4 as your max size, any bigger and it starts getting a bit splotchy covering large scale. A quick breakdown of what I've found so far:
- You can mix a colour, have it dry in the tray, and revitalise it with a wet brush
- Super vibrant
- Can be thinned to be like watercolours or laid down really thick
- Cheap, and each tube goes a long way
- All the best colours can be bought in Series 1 range, no need to fork out for any Series 4 colours
- It dries very quickly, so it can be a bit tricky if you're doing big areas
- Sometimes mixing colours is really strange - one colour can easily dominate another
- Colours dry differently than they appear wet (not a big deal when you keep that in mind)
- The more expensive tubes, while alluring with their colours, are often rubbish. I think they might have *too* much pigment in them
Seriously though, go pick some up and give them a try. I got a set when I was at Billy Blue 8 years ago, and all but 1 tube held the test of time, waiting for me to give them a go all these years later. I've also read stories of people revitalising 4 year old pallets of paint they had lying around.
@Scotty - The wall still looks awesome. At least there's the hand in there somewhere with the spraypaint, way better than just using vinyl.
I think the trick is just getting the right consistency with the gouache. I find it actually needs quite a bit of water added to it, and a pretty wet brush to work with. I tried to watch a tutorial, but the guy was using it straight from the tube with absolutely no water, and it confused me.