Higher ohms, tighter draw: the 1.6 and 1.8 ohm BVCs give the classic cigarette-like pull with 50/50 liquids, while the lower options loosen things up for more vapour. If you are replacing what came in the tank, match the number stamped on your old coil.
Nautilus BVCs are famous for stretching two to three weeks with kind liquids, which is part of why the platform never died. Pod-style Gotek and AVP coils run one to two weeks. As ever, low-sweetener juice and proper priming decide which end you land on.
No, the coil is sealed inside the pod, so the £4.99 replacement pod is the consumable. That single-part design is why the Gotek line is so hard to get wrong for new vapers.