Too Long; Didn't Read
A Checklist of Questions to Ask as a New Product Manager is published by Kishv Kishore V. The first few weeks/months are going to be tough, but this is when the product manager can help lay down strong foundations from a product management perspective. I believe every product manager should look into an early-stage startup when they join. The checklist is not completely sacrosanct, these are some of the elements that need to be borne in mind that many elements of the above may not be in mind in mind.