So you want to run a php page that cycles through the urls and checks if they return status 200? if not then delete them?
You could use curl for this quite nicely!
you can use an iframe and make it’s source one of the records in your database, then when you click next it takes it’s id and increments it and then gets the next item in the database, which then replaces the source of the iframe to the new website.
you could even use sessions for this to store the current website id so when you click next it knows what the next item will be!