Mixing is easy
Mixing something vapeable not so easy
Mixing something delicious = at least a few 100mls of garbage and some time.
vg and pg from essentials depot is pretty standard recommendations. Bull City Vapor, wizard labs, ecig express, vaping zone, and nude nicotine are all great places for flavors, nicotine, supplies, etc. TFA, Capellas, inawera, vaping zone, and flavour art all have great flavors. PG based flavors are easier to start. The alcohol based flavors seem to take more finesse and steep time to get right. At least this has been my experience.
SO a liter of PG and VG along with 120ml of Nicotine solution will get you started and the Nicotine is not necessary to start. Grab a few flavors and read up on the way people sweeten and tweak flavors to get those additives. AP, Marshmallow, Sweetener, Malic Acid, EM, Citric Acid, and MTS Vape wizard are the basic additives. Their are others but these will be important.
You are going to mix some gross things to start. be ready to make the poo face here and there.
Edit - read the stickies about nicotine safety and get a few syringes and blunt tip needles for measuring. And record everything you put in a mix. I made a great custard when I started mixing. Not a clue what was in it.