Rick, typically people only keep one main stem and train it up 4-5', then let it branch out in an effort to promote flowering. Conventional wisdom is that the downward sprawl of the plant encourages more blooms, plus a certain amount of plant mass is required to support these blooms. There have been reports of recent cuttings blooming, but these plants almost always drop the blooms as they are not big enough to support them.

Maintaining only a single stem will shorten the time for the dragon fruit to get to a high enough point where you can then let it flop over. If you have multiple stems, this will take longer. Also, you will need a much bigger vertical stake to support the dragon fruit, they tend to get pretty heavy. You can see some examples here in this thread. Not sure about your pot size, you may want to go bigger now, when the plant gets bigger you won't be able to repot it.

Best of luck.

Your zone is pretty cold, so it might not flower as often. I live here in Kendall Florida and it flower four times last year. It flowered 5 times so far this year. I can't even get my new cuttings to grow a branch. It will flower even without any roots. The cuttings struggle to survive if it produce a fruit, so I have to knock off the flower.