Realistically 3,500 to 5,000 draws once you swap machine-test numbers for human ones: about a week for most people. Twin-tank models like the Duo Mesh split that across two flavours, so each side lasts half as long.
Yes, and that is what keeps them legal: the battery is smaller than the e-liquid supply, so expect to top up over USB-C every day or two. Ten minutes on charge covers an evening.
Usually the tiers price within a pound or two of each other, so choose on features rather than maths: twin flavours and brand names live here, while the 6,000 tier wins on absolute price.