OP, what country is your fiance from?
I did a K-1. In 2018 it made sense for us, and vs today's processing times, it was lightning fast. 8 months from filing to marriage.
Today things are very different. If I was petitioning him today, we would definitely do a spousal visa, for the reasons outlined by the C. Cat.
However, if you do proceed with the K-1, the evidence you mentioned is all we submitted. The boarding passes and passport stamps have historically been completely adequate for most consulates.
Best wishes.