I've been mixing my own liquids for a couple of years and from my experiences i would offer a couple of pieces of advice -
First, the raw materials matter... you might be tempted to snag PG and VG from health food stores, or from abroad, but i've found that US vendors who specialize in vaping supplies tend to be more consistent, and provide "cleaner" bases. This might not be everyone's opinion, but that's been my experience. I actually use the same supplier you are considering for your kit, so you have selected a good one stop starting point.
Second, Nowadays, i only mix in batches of 100ml, or bigger. The batch size helps you to smooth out your flavor profiles and helps with consistency of your flavors... a 2 drop error in 100ml is way less of an issue compared to a 2 drop error on a 10 or 15ml batch.
Third, let the recipes blend. This can be done with time... or can be accelerated with a ultrasonic bath, or some people will even let sit in a warm water bath overnight. All of these basically encourage flavors to come together. Shake and vape will work for some recipes, but the more complex your recipe, the more you'll understand how the flavors will work together with a little bit of time.
Finally, for equipment, I'm mixing directly in 100ml bottles that double as longer term storage, just pouring out into unicorn bottles or whatever as needed. I use syringes to measure and combine, so that's basically all that is in my kit. Using the 100ml bottles lets me measure out my nic, and flavors, then add PG according to ratio, and just topping up the bottle with VG. Very clean, and reduces the "dirty dishes" that come with the beakers and what not. Just personal preference, but my mixing gets done quickly with little cleanup... pluses in my book!
Lots of great resources available, you'll enjoy spending as little as 10% compared to buying liquid, but be prepared for some bad batches while you practice. Luckily it's affordable enough that the mistakes you cannot salvage aren't too pricey while you learn.
