Ref insurance and serial numbers- not sure why your insurer would ask for that, it wouldn’t help anyone or prove anything if your bike was stolen , there’s no bike database. Possibly could be used for accidental damage but most insurers don’t check anything under a few grand, costs more than its worth to do.
I would also read the terms those bike policies often have dodgy clauses, must be locked even when at home etc and are worse than just being covered under the sum insured of contents policy.
Away from home usually the same , must be attended or locked with a 2kg lock which may be ok for commuting but a bit impractical if its a piece of sports equipment.
Anyway good luck with the bike fwiw I like the boardmans and halfords!
Edit: just read the bit about insurers dodging claims, sure it feels like that, you have bought a contract, when its my money I read through the terms before i buy and read it again before I claim, that way there’s no misunderstandings.