You should easily be able to manage Dragon 20. Tomb Lord can solo it, which is the path you should be aiming for - farming Dragon 20 with four food, so you can get both gear and food in one run.
Gear isn't even really that difficult to get by with. You'll probably want him in a Regen / Immortal set, and you'll want him to be reasonably fast - ideally 258 speed, so you can get six turns per every two of the boss, but in a pinch 208 should be fine as well, which'll give you five turns per every two instead. Beyond that, just put stats into DEF/HP, you don't need anything else.
While working on that, just add more people to the team if you can't do it quite yet as solo. For example, adding Wythir will probably make it easier to survive, and Geomancer should make the boss go down faster.
For CB, you probably want to build an unkillable team around Tower. Take a look at the teams listed here, and see which ones you have the champs for: https://deadwoodjedi.com/speed-tune/roschard-the-tower/ and https://deadwoodjedi.com/speed-tune/helicath/ since Helicath and Tower tend to be interchangeable (though not always). If you have none of the champs to make those teams workable, let us know and we can build you a traditional non-unkillable team, but they won't be as good.
