Multiple ERPs

Tmk123 Great question and glad your focus is on developing a strong model, which is a rare thought process for many BI solution developers. Good job!

To answer your question, you surely need to combine all the tables together to keep it one, Let's all purchase order tables are combined as one single PO table, maybe you want to add a company/ERP tag to it so that you can filter on specific company/ERP if you need to.

Now comes to the master/dimension table: you need to still combine the Product/Item table but need to remove the duplicate rows so that these are unique and can have a one to many relationship with the fact tables.

I hope this will give you an idea but feel free to reach out if you have more questions. It is always never easy to answer everything on a topic like this. You are on the right path with the right thinking. Good luck!