Economy
Money is not required to buy one necessity of the soul. It's just really handy to have around at times. The easiest way to earn money is by getting a job. You can see what jobs are available where you are by looking at a city page.
There's no real limit to how much cash you can carry with you in this world, and there's no need to store them safely anywhere where thieves can't get to them.
M.'s pockets are currently jingling with 289,804.40 M$ in them.
Bills
Pay your bills on time. If you don't, they'll turn into failed payments and end up on your criminal record. When that happens you'll either go to jail or end up having to do community service for a long time.
All the bills have been paid.
Bank Accounts and Loans
Money in bank accounts is an investment and is not available whenever you need to pay for something (hotel bills or whatever). Money is never drawn automatically from your bank accounts. Make sure you always have enough cash in your pockets to cover your expenses!