How can I ensure that my busienss idea succeeds?

Bench line: The only way to validate an idea is by executing it. Having competitors validates that a market exists.

Any startup is a set of hypothesis. Any market study, no matter how deep and accurate, supports some of the hypothesis. But the only way to prove the hypothesis, is by actually doing the startup and succeeding.

So, what to do really depends on how much risk you are taking. Does it take a couple of years and all your life savings to launch the product into market? Or can you launch (does not have to be a complete product) in a couple of months while keeping your day job and with minimal expenses?

In the later case, don't worry about studies and research, just launch as soon as possible and find out yourself. Set short-term goals and see how you're achieving them. Add more commitment to your startup as you achieve those targets. For example, quit your day job when you have 100,000 member or 50 paying customers.