RE: Can you link a customer and a vendor record
You need to create them in both Vendors and Customers, but they can be linked via Contacts.
Create your customers, this will automatically create a 'Company' contact for each one.
Go to Business Relations for the Company Contact, Add a new Business Relation Code of e.g 'VENDINFO', (can't use the standard 'VEND' one)

Then, create a business relation for this contact with a code of 'VENDINFO', a Link-to table of 'Vendor' and select your Vendor code.

Now, from the Vendor Card, you can do Vendor > Contacts and see the related Customer Contact.

And from there get to the customer card

You could even set this contact as the 'Contact' for your vendor.
It's not perfect, and the link doesn't work as well the other way around, but a few small mods around this concept would give you a really neat solution.