I'd recommend that before you make any decisions about how to DIY, what supplies to buy & where, etc., etc. that you read the DIY E-Liquid Forum stickies recommended above, and also read as many of the threads below those that you can. In them there's also a bunch of info, tips, hints, questions from (and answers to) others who are new to DIY, too. There are also whole discussions there about Nicotine base, PG and VG, flavorings, methods for making eliquids, suppliers of DIY materials, and lots more.
You'll also find that DIYers have many differing opinions (at times very strong ones) on "the best way" to actually make your eliquids, "the best" places to buy the supplies needed for it, "the best" Nic base, PG and VG, flavoring brands, eliquid calculator to use, etc. Those are all based on our own individual opinions and preferences. They aren't what will necessarily work the best, or be the best choices, for you! There IS no 1 way to make eliquids, nor 1 supplier to use, nor 1 nic base, nor 1 eliquid calculator, etc. that HAS to be followed or used to make great eliquids. Whatever is the most comfortable way, or best priced, or easier to obtain or understand, for YOU...is what matters.
There are some things though that, IMO anyway, every DIYer usually agrees on:
* Care should be taken when handling nicotine base. Also, it and your finished eliquids should be kept out of the reach of children and pets.
* An eliquid calculator should be used when making an eliquid. It will figure out exactly how much of each ingredient you will need to make a recipe, based on specific info. you input into it first.
* First finding several recipes that you want to make, and then buying the flavorings to make those particular recipes...usually results in better first DIY experiences and at less expense, than doing it the other way around.
* Everyone's taste buds are different. What someone else thinks is "wonderful" tasting may be "nasty" to you, and vice-a-versa. Not everyone will like the same flavorings or the amounts of them either. Expect some pleasant surprises, and probably some duds, too, when taking others' recommendations for flavorings and recipes.
* It's usually better to start off with a lower % of each flavoring in a recipe, and add more if you need to. You can always add more, but you can't take it out!
* Asking for information or help from other DIYers is no problem at all. We're all learning new things on here frequently.
* DIY is fun, not really difficult to learn, saves a bunch of money in the longrun, and usually results in having some of the best eliquids that you've ever had!