Hosted VOIP new company

This is the first time I am posting, if I post this not in the right place please correct me.

We are looking to start reselling hosted voice over IP and sip trunking under our own brand.

We are looking for a solution which will give us the opportunity to start with a low cost solution, and as we get bigger we will be able to use the profit to upgrade the application and add custom projects.

Does anybody have any idea if Asterisk is the right decision, can Asterisk handle thousands of users, if yes is Asterisk Business Edition the right choice, or any other provider.

We are not looking just to resell a product, we are looking for a product which will give us full control in customizing and providing technical support, which could be fully accessed by the Web (SAAS), and has separate Web portals depending on the position, and this user-friendly to use.