what will happen if I will renew developer account 6 months later? I know that my apps in app store will not be available, until I renew.

But, from the developing perspective.
what will be the different when I'm developing apps ?
Can I develop and test notifications and iCloud in the development apps ?
See the Choosing a Membership page. Scroll down to Benefits and Resources.

I believe iCloud and Push Notification fall under the 'Advanced App Capabilities' section on that list.

With a free developer account you only have access to: 


Xcode Developer Tools
Xcode Beta Releases
Developer Forums
Bug Reporter
Test on Device