Hi and welcome to ECF.
Basic DIY starting supplies:
DIY calculator for calculating and storing recipes (I use a phone calculator, lots of free ones on the app store for android & pc, not sure about mac)
500 gram scale that measures .01 grams (for measuring by weight, get one that doesn't have auto shut off feature)
PG
VG
(2) 1 L or smaller plastic containers with Yorker caps for dispensing PG and VG, or ketchup dispenser bottles (what I use)
Nicotine or Nicotine Salts (There are PG based, and VG based ones, and blends of both. I stick to PG based because it's easier to dispense, and 100mg/mL as it is easier to store and economical)
Glass bottles w/polycone liner caps (For storing nicotine in the freezer to slow down oxidation, poly cone caps are better than the ones with the foam disks in them)
Empty e-liquid bottles for mixing in
Flavors
Paper Towels
The scale doesn't have to be expensive, I got one on Amazon for less than $15. I like the ones that have a tray on them, search for 500 x .01 gram scale. Flavors, PG, VG, and Nicotine, and sometimes glass bottles, can usually be bought from the same vendor. Many places offer free shipping over $50, so this makes a difference when buying bulky items like PG, VG, or bottles because the weight/size. The rest of the items needed can be sourced locally. If you decide on Yorker tips and plastic bottles, it's easier to get them from the site you are getting your DIY stuff from, but cheap plastic ketchup dispensers can be had from Walmart or Dollar Tree, etc.
Some DIY supply websites I've done business with that I like.
Nicotine Liquid - Vegetable Glycerin - Flavorings -Wholesale and DIY Heartlandvapes Wholesale
PG, VG, Nicotine, flavors, plastic and glass bottles, caps, Yorker caps
Liquid Nicotine - Nicotine Salts | Liquid Nicotine Wholesalers
PG, VG, Nicotine, flavors
Bull City Flavors - Best Prices on Flavoring
PG, VG, flavors, a few plastic bottles (not much), yorker caps.
Feel free to PM me if you have any questions, happy to help.