I would start with 5% Dew for single flavor but I find it's best with a hint or so Lemon Lime. Also 40/60 PG/VG and a few drops Ethyl Maltol for rounding out the flavors. I myself however don't do anything the conventional route all my juices contain about 5-12 flavor elements. Soda type flavors imho need a bit of Cola to taste genuine and I really like the Cola with my Dew. Had asked someone to make a Code Red type flavor a while back but he refused so I made my own.
MDew Red
4.0% mdew
2.0% cola
2.0% lemon lime
2.6% blueberry
2.6% black cherry
1.0% red licorish
1.6% vanilla bourbon/french
1.6% sour
1.0% ethyl maltol
1.6% sweetner
1.6% koolada
??
Which blueberry?
Red Licorice Flavor Concentrate (LA) WL is from Lorann's. TFA doesn't have one.