Hi and welcome, it's great you are starting DIY. It really is one of my favorite things about vaping.
In the beginning, I didn't worry too much about flavor "brands" as they are all different, have some pluses and minuses, and they all vary in "strength" as well, to make things even more unsimple. LOL.
With that said, I read a ton of recipes and tasted a ton of commercial juices to get a sense of what I'd like. I started with "tester" sizes (many of which I am still using I might add, and I've mixed a fair amount of e-liquid by now). I started with single flavor mixes I combined in my tank, to get a sense of steeping times, and "what" went well with "what." I kept some commercial juice around during that time, so that I didn't rush myself. After doing the initial "work" of figuring out general percentages (that worked, for me) I was able to start combining things and knowing "about" how long my longest flavor needed to steep. For example things like custards and cremes need to "steep" for a while longer than berries, fruits and some candies. Etc.
Whatever method you use (and there is certainly nothing wrong with following an existing "recipe" as it were) keep notes, keep track of times, how things taste, and etc. Nothing worse than making a "perfect" mix and then not being able to replicate it.
You may also want to look at some "one shot" flavors, which are standalone flavors (I am of the opinion that some of them can be improved by adding flavors) but some are great alone. They can usually be shaken and vaped, without much or any steeping time and it's nice to have some "success" right away, as you start the process of learning about flavorings.
Best of luck, I'm sure you'll do fine. Nothing wrong with a starter kit at all either, although I did not begin that way, but any beginning is a good beginning. Keep asking questions as you go, and I'm sure your skills will develop as you continue mixing.
Happy mixing and I hope you find success!
Anna