The API does support this, but we have yet to add an option to change it from the default of 10.
There is a search box on the Query Log page, and if you click on any of the clients under Top Clients on the main page it will show you the queries made by that client.
Youtube has been very difficult to block, and the effects of Pi-hole on Youtube have been very diverse. The banner ads have been blocked, but the video ads are either blocked, blacked out (like what you see), or are still there. There are a few threads trying to figure out Youtube ad blocking, but it is still unsolved. How do I block ads on YouTube? Youtube 10-Second Black Screen