Welcome to the forum! You are on the right track. Cycling with a bike you already have is a great way to burn calories, but you do need to do it a lot. The brakes you mention are a non-issue - they only help you stop!

If you are not into racing or something, I wouldn't worry about tracking progress with technology. Your scale can do that just fine. So will a regular clock. Your body will also tell you when big hills start to feel like small hills.

Personally, I like the routine plus model. Commit to specific weekly time/miles that you will do no matter what, and then add errands and fun rides on top of that.

You are also young, so if you ever overdo anything, you will recover quickly.