You don't need any special business account; any bank account is fine. There isn't really anything special about the apple developer forums (in my opinion), I think the main thing is being able to test with a device.
Signing up for the developer account while developing as opposed to after completion of your app is a personal preference.
If you get it now you will start using up the 1 year membership. You won't be able to test your app on a device however, only on the simulator. Depending on your app this may be fine, but some things are untestable without using a device.
My first app was a game and I only purchased the developer account when it was "complete". On the simulator i was used to the app starting in one second, however on the device it took 30 seconds to load and performance during use was unacceptable.
It's quite possible to develop an app with only testing on the simulator, but you will never be sure that it works exactly the same on a device.