Two questions about your drone, and this points you to the right page on the CAA’s own site. The CAA is the authority on this — always confirm with them before you fly.
Not sure? It is usually printed on the drone or in its manual. Many popular models sit just under 250g.
A toy drone with no camera is treated differently from one that can record.
Registration is handled entirely by the CAA. DroneChecker cannot register you.