Funding is the most important thing if you want to start a magazine. You will need money (lots of it actually, if you want to start with a broad reader base) to finance the cost of printing, distribution, and to pay for your writers’ contributions.
How much money you will need exactly depends on the number of copies that you want to print. It could be anywhere from $10,000 for a community magazine that you write yourself to $1,000,000 for a national magazine with a few writes under your payroll.