What if the Identity Provider asks for 4 attributes e.g. First Name, Last Name, Email and Principle Name? Will it matter as EZRentOut only looks for First Name, Last Name and Email?

The extra attribute will not be an issue. However, while configuring, you’d most probably have to map the exact attribute names of the first name, last name and email fields that are provided by the Identity provider in the Settings → Add Ons page.