Help.. creating a map/dungeon or finding them fully stocked

I have been a D&D player and DM for some time.. 1e.. I'm old.. However, I have recently bought into 5e and am looking to more to the digital world here shortly. The idea that this could save me a ton of time is great.. but, it also looks more like I will be trading time to be used differently, instead of drawing the map on paper, its done in the system etc.. I really want to know if there are free module, campaigns etc that other people have created, be it members or otherwise. I love the idea of the Mad mage module purchased and ready to go but, are there free ones.. where. how do you import them.. what am I looking for. Do I need to buy the monster manual if I have the physical book in order to stock my own dungeons or do I have to create everything. 

Currently, there are two free 5e adventures that I can find. <a href="https://marketplace.roll20.net/browse/module/40/the-masters-vault" rel="nofollow">https://marketplace.roll20.net/browse/module/40/the-masters-vault</a> <a href="https://marketplace.roll20.net/browse/module/5353/adventure-preview-explorers-guide-to-wildemount" rel="nofollow">https://marketplace.roll20.net/browse/module/5353/adventure-preview-explorers-guide-to-wildemount</a> The Master's Vault was designed with helping to learn Roll20 in mind. You might also want to go through the Roll20 Crash Course.&nbsp; <a href="https://help.roll20.net/hc/en-us/articles/360039223834-Roll20-Crash-Course" rel="nofollow">https://help.roll20.net/hc/en-us/articles/360039223834-Roll20-Crash-Course</a> Adventures on the marketplace generally have everything you need to run the adventure as written. They include the adventure text, maps, character sheets tokens, and everything else set up and ready to go. The two adventures above will give an example of that. There is a large amount of work that goes into creating an adventure for the Roll20 marketplace, so many of the adventures on the marketplace are actually good value for money if you want to run an adventure that is ready to go. Otherwise, there are lots of art assets on the marketplace and elsewhere online. The advantage of buying on the marketplace is that the art from those purchases does not count against your online storage.