Glad you are making progress.
On the Queries you need to seed all of the query fields at once. There is no way to do multiple, sequential queries which i think you figured out.
Are you sure you need to keep the returned rows in two places? What exactly do you want to do in your form?
If you want to have a drop down list or display them you can do this with the datafields. I would assume the user would select which of the returned rows to keep or use. Sometimes I have added a selection field for this but you could have a button which copies a row from one node to another.
Are you wanting to database the parts list or bill of materials? If that is the case you are going to run into the InfoPath limit of one submit data connection, which you have already used for your parts. You may want to look at using web services and the database accelerator to make this solution easier for you to create and and more powerful for your users.
Qdabra Database Accelerator Suite Version 2.0 - Developer