Sap cloud for customer scoping and implementation

Hello Dear experts,

I have couple of questions I would be glad if I was able to hear your recommendations.

1. Our company has already implemented Cloud for sales. In Business configuration work center I have only one project called "First implementation" with the status of Started. My question is : when I need to add additional elements from scoping should I edit the same project scope ?

2. If there are multiple companies under the one company should they have different tenants or they can share the same tenant? what is the best practice in this case ?

Thank you in advance,

Best regards.