Run some small tests. Here is a super simple method.
1. Put 20 drops of VG into a small bottle.
2. Put flavor drops into the bottle based on the percentage of flavor you want to use.
3. So if you want to test 20% of flavor that would be 4 drops of one flavor or 1 drop of 4 flavors or 2 drops of two flavors

4. The VG drops are thicker than your flavor drops so make a small adjustment here for your total volume.
5. Mix it up and drip it onto a wick and coil and vape.
If you like it, make more. Have fun! Good luck!
This method is easier and more efficient than mixing 3-5ml samples. I also do not enjoy measuring .025 mls in a 1 ml syringe
It's super fast and you can get many combinations tested quickly.
As far as what flavors go with what flavors, there are many places here to figure that out. I simply makeup my own combinations.
Peanut Butter does go well with banana or caramel or double chocolate coconut though