Question on imports with foreign keys

Hi,

suppose you need to import a csv with standard ciolums like name,
adress, phone, ... and some additional text columns that need to be
split off into referenced tables.

Those lookup-tables will only be needed for a project with limited life
time so I create a schema that might be called "project_x". There I
create the necessary lookup tables.

The core of the import will be added to the customers table with
unlimited livespan. The customers table has a PKey id which is a serial.

I don't want to add FKey columns into customers for the new
lookup-tables so I create another table in project_x "projectinfos" that
stores those FKeys and another FKey that references customers.id.

First question: Is this a stupid aproach?

If not:
How is the easiest way to to find the customer.id of the new customers
so I can insert the projectinfos?