Yes, you can create Jobs and then schedule them for daily, weekly and monthly occurrences.
Yes, a Job can be assigned to multiple fieldworkers.
Yes, Audits can be easily created and executed using EyeOnTask. Audits can be of different types, be it an Internal organisational level Audit or Audit associated to monitor equipment in a Contract.
Yes, EyeOnTask integrates with QuickBooks, thus giving your a way to sync your clients and invoices.
Yes, Customer portal comes with EyeOnTask, Admin can enable or disable the Customer Portal from the settings.
Job is a single entity whereas a Contract is a combination of Jobs, Invoices and Audits.
Inventory Items can be sold and invoiced , thus you can maintain their stock. Equipment/Assets on the other hand are rented or leased and so are kept intact when returned.
No, Both are different apps available on google play store and App Store.

Following are the links to it.

EyeOnTask App for Fieldworkers Android

EyeOnTask App For Fieldworkers IOS