Sure you can use a street bike to do Flatland, just be aware, though, that it will be a lot harder to do Flatland with a street bike than if you were using a specialised Flatland bike.
I started riding Flat with a Hoffman Disruptor, and I did pretty good with that. I ride only Flatland, though, so I got myself a specialised Flatland bike after 6 months of riding.
Most people who take up Flatland will quit after a few days or weeks, because it's so frustrating, so I would not recommend getting a Flatland bike if you haven't tried Flat before. Stick with a street bike, and if you find you really wanna get better at Flat and stick with riding Flat, THEN you can get something more specific, but if you decide Flat isn't for you, then you haven't lost anything, because you still have a great street bike to use for.... riding street!!
I assume you are female..?? If so, then the Fit park 18" will be perfect for you, size and weight wise. Flatland will also be a lot easier on that than a regular 20" bmx, because the Top Tube length, and the wheel base length, will both be shorter, making it easier to lift the bike onto one wheel, for Flatland tricks.
Hey, if you wanna try some Flatland tricks, go to Youtube and search ' vfi flatland ' , and you will find a ton of clips with 'How To's' on Flatland tricks. VFI stands for Virtual Flatland Instructor. Start with easy tricks like the Steamroller, Fork Glide, Bar Spin, Peg Wheelie, Trackstand.
Hope you have fun riding BMX, it's an awesome sport, and great exercise, too..!!
Email me if you have any more questions.
