@jbrines
If you move to a document library the design is a little different. Yes, you can connect to the library just fine in PowerApps. However, the simplicity of the Attachment control kind of goes out the window as you are not working with the attachments any longer, you are working with real documents. There are a variety of ways to go about getting the documents into the library from the App and there are numerous videos and forum posts on doing that.
NOW, depending on your data design, you can either continue to have one list that has the information you need in it (and this is probably recommended as you seem to indicate that you will have one to many records in the library) or put the metadata directly into the library (libraries are really just lists in SharePoint as well).
I would say that if you keep two lists (list and library), at least have a column in the library that will contain the ID (or some other unique aspect of the master record) in it. Then in your App, you simply filter the document library by that unique column.