@AnthonyB - Normally when I create a recipe I do so in a 10ml bottle. The flavors I choose all get started at pretty low %'s. That way I can add more as needed and I don't waste. It's much easier to be able to add more than to try and dilute an over flavored mix.
Usually when I create something I will only start with a couple, 2-3, flavors and get those right where I want them before I start adding more of the flavors I want. With DIY I tend to think in terms of an upside down pyramid. The flavor you want out front is at the top, everything else is layered down to the point of the pyramid. Works for me.
I like creating my own recipes. There will always be the duds that just don't work out. Even with those I do try to add other flavors to try and improve them, and learn from. Sometimes those just don't work out and I end up tossing them. It happens.
As you get to know your flavors you will learn over time what works best with what. Take great notes with everything you do. Those will come in very handy. If you see others posting notes and info, grab those too, they are useful and do come in handy as well. I'm always grabbing folks info and popping them into text files.