Does foreign table doubles server storage?

I'm building a SaaS which in one database I will have a large targe (something like 50milions rows), and this table will serve information for all the customers of the system. But, that SaaS will be a multi-tenant / multi-database software, were when a client register in, we will provision his own database to access AND create a foreign_table for that large table outside of the database... Question 1: Is is the best approach? Creating a foreign table for each customer may result in a large usage of storage of the server? Question 2: The original table has kind 10 others indexes (most of them btree), and with the foreign_table for the customers, those indexes will work properly?