Which is best Content management for making web hosting site and integrate free billing software as well.
I would recommend building a website in WordPress, with a good theme and then getting yourself WHMCS. http://www.whmcs.com
but WHMCS is not free to integrate with wordpress and wordpress don't have any plugin for integrate with whm server
For serious business put some money on WHMCS as investment, It will help you on long run and find a free template for the WHMCS. You can also use joomla as it has a good component integration with WHMCS.
Thats sounds good. Then please buy whmcs and speed-up your business. I'm doing this business more than 1 year and some month ago I've purchased whmcs, it will take some time to learn how to operate but whmcs is good. Before using it I was using box-billing, it is good too but for free version you can't add more than 5 products.
No it's not domain based license and my experience actually i started 4 years ago with another domain but then after 1 years i stop selling hosting but now i again started few months back ago