1) In the checkout wizard, on the shipping section, leave the "I will provide shipping" options checked. you can leave the provider set to none, and leave the base rate and incremental rate set to 0.
2) you should be using the Default - Sage Pay preset.
On the bindings panel, there should be a binding collection titled "Sage Pay VSP Server Authentication"
under that binding group, you should see the bindings for the
Vendor Transaction Code
Sage Pay Transaction ID