SAP Web services integration configuration process and testing

I am working on integrating our SaaS application with SAP R/3.

We, as a startup, don't have in-house SAP products, licenses, or ABAP developers. We are planning to go with Web services.

1) Can you help me to understand the procedure, testing, and maintenance?

2) What changes do we have to make in our data structure?

3) Is there any template available for the data structure?

4) Is it possible to do web services without Netweaver?