I have over 3000 books in my library and still don't have all the books I would like to have.  It really takes a lot of time and study to know which editions of which books you want to get, and which have not been edited.  Banner of Truth puts out some great reformed books, some of them of great value, but in the book Sovereignty of God by AW Pink they edited out some of the most important chapters.  In that book you would want to get the Baker House edition, which is the complete and unabridged book.  There is a series of paperback books that you can find at some bookstores and online called the "Puritan Paperbacks" which are very valuable, but some of them are abridged versions and some are not.  You'll have to check on them and see which are abridged and which are not.

As far as the Reformers (or Reformed, Puritan or Calvinistic authors) you can't go wrong with anything written by AW Pink (except his book on The Antichrist, which he also does not recommend), or John Gill.  Both of these authors are not technically "reformers" because they wrote much later than the Reformation, but they are both Doctrines of Grace teachers, strong on Sovereignty and Responsibility.  I would recommend:

The Mystery of Providence by John Flavel
The Ten Commandments by Thomas Watson
The Puritans on Prayer from Soli Deo Gloria books
The Valley of Vision
Absolute Predestination by Jerome Zanchius
The Sovereignty of God by Pink
The Attributes of God by Pink
anything you can find by John Gill (especially read his online articles about Baptism)
The Sincere Convert by Thomas Shepard
Death of Death in the Death of Christ by John Owen
Freedom of the Will by Jonathan Edwards.

Some of these are available as books online for sale, and some are available online to read, so do a good search. This list, if studied carefully with your Bible will take you some time to get through, so I wouldn't recommend buying a bunch more than just this in the beginning.  I have all of these books, so anytime you are here, you may have access to my library to read them and then you wouldn't have to purchase them.  The first I would read is Sovereignty of God, then the Mystery of Providence and Absolute Predestination.  After you have read 3 or 4 of these books, make sure you read The Ten Commandments and The Sincere Convert - they will stop you from falling into the Calvinist trap of pride, presumption, arrogance and antinomianism or hyper-Calvinism.  The hardest books here to read are Death of Death by John Owen, and Freedom of the Will by Jonathan Edwards.

Let me know if this helps, and of your progress as you go along.

Your servant in Christ Jesus,

Michael