Welcome Azzaziah!
The RTS kit has some good stuff in there. I googled "diy mixing kit e juice" and found a number of options. Heartland Vapes and DIY Flavor Shack also seem to have "goodies" combined.
I use disposable pipettes, and when I first started, I recycled my bottles from the juice I purchased until I could start stocking up on glass bottles. I mix in my bottles, although many subscribe to the philosophy of using beakers or other larger containers in which to mix.
Your choice of flavor bases (LorAnn, Capella, Flavour Art, TFA, FlavorWest, etc.) might dictate whether you can get by with "single-flavor" mixes or if you need multiple flavors to complement in a mix. I have a few Cap flavorings that I really like as stand-alones. My TFA flavors - I need a number of different flavors to comprise a mix.
I'd start with smaller sizes of flavorings. You can ALWAYS mix unflavored - just get a nic base and some PG and/or VG to get the ratio and nic level you want. If you add some flavoring to THAT, you'll slightly dilute the nic level and may alter the PG/VG ratio somewhat, but you may not even notice the difference. TJ has great advice on KISS. Sir2 has great links for reference.....
Good luck and vape on
