I'm looking for a little info on how to go about creating a new Third-Party Portal for a contractor/vendor/employee who is not a Method user...
These people do not have to be Method users they just have to have a portal setup where they can register as Portal users.
If I include the QuickBooks_Time Tracking Screen, I see it looks at the Entity table, so a filter could be created, and all other necessary fields should be available. For expenses - is there any way for expenses to be submitted by a non-user?
Since you're thinking about using the Entity table (would also work with tables like; Customer, Vendor, Employee or Other) the portals will have built in filters to only display that particular Entity’s related records.
You're correct about this being customization work but it may not be as much work as you think. Feel free to contact us for consulting if you require assistance.
In the meantime I'm going to link you to a few webinars that you might find helpful:
Getting started with Tables and Fields
Introduction to the Customization Screen
New Contacts Portal with Payment Gateway Integration