You don't have to make a limited company but it might be necessary for some contracts. You might also have to carry insurance. An umbralla company might also be appropriate for you, especially if you're not 100% sure. It has been a few years since I quit contracting (to start my own company) so some of this stuff might be old.

Definitely read about IR35 and how it might affect you.

In all cases, an accountant can answer these questions for you, even if you're not sure you want to commit.