Bulk Download PDFs from Google Scholar
I know one relatively simple way.
Zotero + a Google Scholar Zotero plugin for you browser (typically, Firefox or Chrome).
Bibliographic manager. The program helps you to download bibliographic meta-data together with the PDFs (if they are open).
So, you may "save" all the needed papers to "My library" in GS (if you have several collections, you may assign a special "label" to each collection). Then, when you have all the papers in one list, just export them all to Zotero. Whenever possible, Zotero will download a PDF.