This should be a hard stop of how many pages should be scanned. It is recommended that you do a page count scan prior to setting your limit (using the Just for counting pages Checkpoint), if you intend to scan your whole site.
This is a count of how many pages to scan in the order the scanner encounters them. If you want to scan 50 of your top level pages you should set your Level to (1 or 2) to try to get the closest pages. Running a 50 page scan at 20 levels may only search one tree of your site, and thus the results may be undesirable or confusing.
This count is what is used to show progress in your scan. If you set the Max Pages to 100, each percent of completion will be 1 page scanned. If your site only has 316 pages and you set your Max Pages to 500 the scan will end abruptly near 63%.
This is a designation of how deep into your site you wish the scan to travel. You may want to consult your sitemap or create one if need to determine your max Level and you wish to search your whole site.
It is not recommended to set your Level to its maximum (20) as this will drastically increase the scan time and may not serve the function you are looking for.