How would you proceed to validate a bunch of ideas on adwords?

If you wanted to choose between a multitude of ideas, with landing pages already created for all of them.

Would you care about the click rate? or just the conversion rate?

This is more of a statistics questions, but how many clicks would you need on each page before comparing conversion rate?(with enough certainty)

Do you think a domain name is important?Or could I reuse the same one or a subdomain?I want to spend as little money as possible to test as many ideas as possible