Just wanted to say good luck!
I got destroyed in Legend last week. But I managed a couple defeat alls and the DM reward was 30. The droprate for DM was about 30%. It's either the same or higher in Legend. And it will take the equivalent of 47-50 defeat alls to put you comfortably above the 9100 mark. So ~400DM per season.
With the 25+100+200+300 you get for climbing, plus the top 500 reward, you're looking at 2425DM. Add anything you get from Tower, daily rewards, calendar, etc. and it should be possible to make a profit if you're buying @30% off. In the very least, it's possible to fund yourself without buying DM at all. Which I think is great.
With natural energy and a little over 20 crowns, you should still peak above 9100 after all the bleed.