Hi and welcome to our hobby.
Mixing your own can be a lot of fun. You can mix other flavor juice with other juice and if they are the same strengths you won't change the nic concentration, as mentioned use the box at the bottom of the calculator excel sheet to see how diff strengths mix (easier than doing the math yourself) So you see mixing is not just for flavors, you can mix whatever nic concentration, pg/vg ratio with any flavor by starting with unflavored nic juice at a higher (36to54+ mg) and adding PG orVG and flavorings.
find pure flavoring from Loranns, these are food flavorings you can use to flavor juice or your food recipes (the orange oil is oil and may not be good for keeping your atty clean) you can order all their flavors from their website or find select flavors at Hobby Lobby.
If yu mix 1ml of 24 mg juice with 1ml of VG or PG you will get 2ml of 12mg juice
Mix small test batches first before you waste precious juice. If you like menthol, menthol crystals can overpower any bad tasting mix.