Monster and dungeon rewards are the primary income sources in this version, then once the merchant title improves, money is more or less infinite.
For the crashing, does it give an error message, or does it simply dump you out of the game? Without an error message, there's not much I can do other than recommend a reinstall... there's a bit of a memory issue I've seen in the past with android, but it should be pretty much corrected. If nothing else, I'm migrating the code into the newest version of Ren'Py with the next version, so that may resolve some compatibility issues.