Will ios 7 work on my iphone 4?

Tell me fast i have to buy it

Yes, it will.iOS 7 will be supported by iPhone 4, iPhone 4S and iPhone 5. But I recommend the iPhone 4S than the 4.

Yes, but it won't be released to the public until the fall. If you want to install it early, you need to register your UDID with a developer account through a site like http://www.udid.in/.It's $5, and then you can try out the new OS before everyone else. That's how I got it on my 4S.