Mega Menu

I am sure you can control the menu by creating your main/home menu then as you create new pages you simply pull the page in under the main folder and it becomes the drop down.  There is a help page for doing that. Look for "drop down menu" in the help topics.   I have not tried to put a page under a page under a page though.  You can also create links within a page to a "not visible in menu" page that you have, which is a bit "neater".   Too many sub menus make it harder to navigate, especially on mobile devices, and will reduce your site's visibility on search engines because it's not as easily searchable, though.  

Hello,

Yes, you can have up to 4 tiers in your drop down menu. You can do that by going into your Pages settings and dragging pages to the right, under the page you want it to drop down under.
As Lynn mentioned, please keep in mind that the more drop downs and sub-pages you have, the more difficult it will be to navigate your page, effecting your site SEO and customer experience.