With that % rate it's All Risks cover, but of course check the terms of the policy. If you are adding items that were previously covered under general contents, you may be able to reduce the contents sum insured. It's also likely that the excess for items covered under All Risks will be lower than the general policy excess.
Regarding covering bikes, if the bike is kept in the house and no cover is required outside, most insurers allow bikes under general contents and there would be no extra charge other than the increase in the Contents sum insured, which would be much lower than adding as a specified item - however check your provider to be sure.