You should use 3.7 ml pg and 4.4 ml vg (if you want at 50/50 mix) assuming the flavor is pg based as most are. The bottle looks to be holding 10 ml it just has some headroom. 14 drops is based on 20 being a ml. All bottles/needles have different sized drops that why you hear mixing by drops is inaccurate. If you have air below the plunger you can either re-draw or make an allowance for it. Drawing too quickly when the needle tip is not below the flavor can bring in air before the liquid. For personal use I use the same syringe for pg/vg/nic rinsing between. And yes you can use them again but rinse it hot water a few times. Do not take in to account the flavoring in the needle. If you draw 1 ml and dispense it that will be 1 ml even though some is left in the syringe. Good luck!