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?