I’ll tell you my experience. I met my wife in May 2018. I visited the first week of July 2018. I had proposed to her during my stay there. I booked another Trip to see her in October 2018. I filed for a K-1 Visa in July when I returned from my first trip. When I sent in all my evidence, I also sent in my proof that I had plane tickets to visit her again in October.
The simple answer is yes, one visit (from my experience) was enough to get the ball rolling. By the time my wife (fiancé then) had her interview we had two visits under our belt for evidence. Keep records of everything. Where you eat together, hotel stay receipts. Take plenty of pictures. A lot of work, but we’ll worth the wait for someone you love. Be sure to tell them how you met. Tell the truth. You don’t want to be caught in a lie. We just had our second Wedding Anniversary! God bless and wish you the best.