I've bought a few different bottle sizes cheaply off ebay but now I use 30 or 60ml for testing sizes and 250ml once I'm happy with the recipe. On the 250's I bought, the ends of the drip tips needed to be snipped off first which was fine but also the plastic was a bit big for the kidney slots in my tanks but I sorted that out with a pencil sharpener and now they work perfectly and actually hold about 1/2 a pint of juice.
As others have said, don't bother with syringes and just stick to scales. Look for some that weight down to 0.01g.
I do find pipettes helpful sometimes when I'm refilling my 30ml flavour bottles because they have drip tips but I buy the flavours in 100ml bottles that don't come with a drip tip.
The only other bit of kit I would highly recommend is a 5ml measuring tube. You need to weigh the empty tube first then with any new flavours I buy I fill up the tube to the 5ml line, subtract the weight of the tube and then divide by 5 which gives me a pretty reliable weight per gram figure for all my ingredients.
I also like to use a speadsheet to keep all my recipes and all my flavour stash recorded, including the weight per gram numbers.
There are also lots of good recipe calculators but personally the only one I ever use is the one on here.
https://www.planetofthevapes.co.uk/e-liquid-recipes/mixing-calculator.php