What do I need for Dungeon of the Mad Mage? (D&D 5e. Questions)

I am thinking on starting up on Roll20 and running Dungeon of the Mad Mage. I am an experienced GM but have never run in Roll20. I assume that I would need the D&D 5e. Starter bundle with DMG, PH and Monster Manual and the DoMM senario. But how about Volos guide to monsters, Xanathats guide to Everything and Mordekains Tome of foes? Can I run without thoes three books, even if some monsters are from thoes books? Can players be Character options from Xanathars?

If you're willing to enter everything by hand, you don't need anything! However, it's probably a lot easier and saves a lot of time by getting the books you want to draw from. Or you can be like the kind of weirdo I am, and get books and still spend hours customizing everything! Getting the PHB allows you to share it with your players and speeds up character creation and a lot of play. Getting a Roll20 asset gives you the ability to drag and drop game elements onto the map and onto characters rather than entering the information manually. And yes, getting Xanathar's guide opens up automated character options if you share that compendium with the players.

Thank you Dr DM ;-)

Just a point to consider: If you are running the DotMM module from Roll20, you do not need the Monster Manual. The module comes with the full-featured ready-to-play sheets and tokens for every monster in the module. And there are a lot of them in that module. Also, any DMG-specific rules (such as madness tables) that are referenced by the adventure are in usually included as well. So the DMG  might be considered optional. (It was only released this year, and people have been playing that module for a lot longer). I would suggest the PHB, and add Volos or Xanathars if you want some of the optional races and classes. Check out some of the WotC bundles in the Marketplace.

Good things to know, thank you Keith.

I think just the module, Dungeon Of The Mad Mage.  It works fine stand-alone. The D&D 5E "SRD", the open parts of the rules, is already included with roll20 in a feature called Compendium, that's before you even buy PHB or DMG.  Likewise the D&D 5E character sheet is already included for free.