Your cousin needs to show proof of funds and may not be possible to use a letter from you unless if you can pay off their full tuition fee and provide a letter to state the support of living expenses.
Every application is different from others. In some applications do more checks like social assistance etc if the sponsor doesn't have a good-paying job/funds to support and different VO across the globe has different policies (like LVO is the slowest office) and there are other checks like...
AOR is acknowledgment from immigration office that you application check is completed (like forms,signatures,documents etc)..
when you trying to link sponsor application use `2` for number of applicants as both sponsor and PA are in the application.