Hi,
1. Tenant in a cloud world is basically installation in on premise world. So for your app you will need a tenant of identity service. How to do it as a SAP employee? I have no idea. Here is description for SAP customers. Basically, you have to go trough sales rep.
2. Here you will outsource identity management to this service. The service provides forms for self registration (if configured in admin console). So I assume that somewhere in admin console you will be able to get a link for your tenant.
3. You can configure which attributes will be collected by identity service. You can also configure which attributes will be passed with SAML assertion. More info here. I believe that xsjs API will give you access to those attributes.
Cheers