R12.1.3 - Best Practices around implementing shared services billing

We are on R12.1.3. We are implementing shared services billing, where 3-4 shared services will take care of prac;e related business transaction services like processing payments, cash application etc. of all operating units across the globe. The shared services would bill the operating units using the project internal billing functionality.
We want to know the best practice in shared service scenario for  -

1. Inter-Project Billing vs.Intercompany billing

2. Whether we should create one expenditure type per business transaction service(for e.g. cash application) or group multiple business transaction service in one expenditure type? We use the non-labor rate schedules to bill the operating units using a bill rate for each expenditure type.