My complete unprofessional opinion:
I am big against big cliffhangers at the end of books.
Personally, as a reader, I find it frustrating.
Leaving questions unanswered is good. Leaving the characters journey unfinished is good.
I firmly believe leaving the reader waiting for the metaphorical "other foot to drop" just builds frustration and is an unsatisfying conclusion to all the time spent reading the book.
Such large cliffhangers are okay between regularly updated chapters. So if the wait for the resolution of something climatic will only be like a week or so then I think it is fine. but if the reader is waiting a LONG time for the next book- it feels bad. And I am personally less inclined to wait around and care about the next novel.
The big climax and/or story arc of the first novel should be resolved in my opinion but there should definitely be questions that linger in the air to keep a reader interested for the next installment.
So that being said I think it depends on how big a cliffhanger you are thinking about leaving book 1 at.
As a reader, I think leaving some things unresolved is good an interesting but Big cliffhangers are frustrating and leave me feeling bad.