Here’s my recommendation:
Liitokala Lii 500 or Zanflare C4 charger - cheap 4 bay analyzing chargers. These let you test all the batteries you get to make sure they are legitimate, and lets you monitor battery wear over time.
If you think you might want to venture into the realm of 2000+ lumen lights, I would suggest getting Samsung 30Q batteries in button top form. If you plan on sticking to <2000 lumen lights, Sanyo NCR18650GA batteries will give you slightly longer runtimes, at the expense of lower max drain (not an issue if you are looking at <2000 lumens). Can get them from Liionwholesale.com, IMR Batteries, Illumn, or Mountain Electronics.
For starter lights, I would suggest the Convoy S2+ in Desert Tan, and the Convoy C8 Clear, both ordered directly from the Convoy store on Aliexpress. Would suggest ordering the S2+ in the 7135x6 configuration, and get both in the 3A tint. The reason for these particular models is they come with the improved Biscotti firmware (the Desert Tan model on GearBest only has the old firmware). They will also give you a decent idea of output, beam profiles and form factors, and you can use that information to influence future purpose.
I’d also throw in an Emisar D1 right away, as it will sit between the S2+ and C8 in both size and beam profile.
Edit: One more thing - headlamps. If you want a decent budget headlamp, I’d suggest the Skilhunt H03. Can be used as a flashlight, or put in the headband for hands-free use. Can come in surprisingly handy, as a lot of the times when you need light, you also need your hands free for something else.
Once you’ve got experience with those lights, then you can decide where to go from there.
Want even more output and good runtime? The BLF Q8 can do 5000 lumens, and runs on 4 18650s.
Want tons of output in a tiny package? The Emisar D4 can do around 4000 lumens, and is even smaller than the S2+. Can order the 18350 tube for it if you want something comically short.
Want something similar to the S2+, but more compact and “premium”? Check out the Zebralight SC64.
Want more throw than the C8? Check out the Emisar D1S.
After using the S2+, do you think an 18650 light is too big for everyday carry? Maybe you need to check out 14500 or 16340 based lights.