When I was fully in the closet, in denial to myself, I didn't handle it well at all. Once I was out to myself and a few people close to me, I still found being in the closet to everyone else to be hard. It was bearable only because I knew it to be the first step of a fulfilling journey. I don't have any survival tips except that transition was my way out.
My support network started with my wife. I knew I needed her on board before even starting therapy. Immediately after telling her, I came out to a neighbour who I knew worked with LGBT kids. I figured she would be supportive and could help me find resources in my area. That led me to getting into therapy, and also to finding a support group in the nearest big city. If you don't have a helpful neighbour, any city would have an LGBT organization that could connect you in the same way.
Testing the waters... Nope. You can't dip your toes in. The first one, you just have to dive right in. Pick someone you are close to and whom you trust. There are sample letters and many coming out tales on these forums to help with how to present your news. I chose my wife because that is just how our relationship works: she had to be the first to know. Other people, in other relationships, talk to a therapist first, and get help from them with planning their coming-out strategy. There is no one right way to do it. You have to decide what will work best in your situation.
This is all about who you are. How can you be wrong about who you are? Your therapist will help you decide whether or not you really are transgender, and what is your best course of action. But you are who you are. The feelings that brought you to ask those questions are real. You didn't imagine them. That is your assurance that you are real.
It is normal to have doubts. Cisgender people never question their gender. Doubts or not, the fact that you are asking the questions strongly suggests that you are trans.