Send/receiver via SOAP/HTTPS/SSL - help needed!!

Hi all. I have two interfaces in development, one that needs to receive customer orders from our website and one that needs to send data to a third-party financial institution. We are using an R/3 4.7 backend and XI 3.0 SP17. I know we need to use SOAP adapters and that certificates will be required for both of these interfaces. However, no documentation on this topic (including SDN threads) seem to contain a step-by-step guide on how to use these adapters to create/talk to web services.... are there any step-by-step guides out there?

Specifically, I need to know:

1. How do I know if I need to use certificates?

2. What purpose do the 8-week test certificates from SAP serve?

3. Do I need a WSDL from the third-party receiver to import into the Repository? The finance house hasn't heard of WSDL... they just want an 128-bit encrypted XML file

4. Are there any issues with SP17 in this area?

5. Has anyone out there done this and can provide with some simple steps for my two scenarios?

Many thanks for any help - this I'm sure isn't that difficult but its only easy if you know how...!

Stuart Richards