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While these plants will normally die down for winter dormancy, thus, not requiring too much pruning, since yours is quite large, cutting it back by about a third (or even half, if not more) might make it easier to fit the plant inside. Here is an article or two on overwintering passion flowers that you may find helpful: https://www.gardeningknowhow.com/ornamental/vines/passion-flower/preparing-a-passion-flower-vine-for-winter.htm
https://www.gardeningknowhow.com/ornamental/vines/passion-flower/passion-flower-winter-care.htm

It really just depends, which is probably why you are hearing conflicting stories. First, it depends on the variety you are growing. A standard passion flower can winter in Zone 6 in the ground, but many of the fancier varieties need Zone 7.

Second, because yours is in a pot, you should be aware that you should treat plants in pots as though they need to survive one zone lower than your current zone. This is due to the fact that containers lack the insulation that plants in the ground have. You can combat this somewhat by placing the container near foundations and mulching, but it is still going to be more susceptible to temperature fluctuations than plants in the ground.

Third, is when you are in a border area, you never know what winter might throw at you. You may have several Zone 6 winters and the plant would be fine and then get hit with a Zone 5 winter, which would kill the plant.

Do you have an attached garage or basement that you could store the container in? This would be your best bet for getting the passion flower to make it through the winter.

These articles will help: https://www.gardeningknowhow.com/ornamental/vines/passion-flower/passion-flower-winter-care.htm
https://www.gardeningknowhow.com/ornamental/vines/passion-flower/preparing-a-passion-flower-vine-for-winter.htm

It sounds like it may have too much nitrogen and not enough phosphorous. Plants need a balance between phosphorous and nitrogen to bloom well. I would recommend giving it some bone meal to increase phosphorous.

Depending on your circumstances (container or garden plant), here is an article or two that you may find helpful: https://www.gardeningknowhow.com/ornamental/vines/passion-flower/passion-flower-winter-care.htm
https://www.gardeningknowhow.com/ornamental/vines/passion-flower/preparing-a-passion-flower-vine-for-winter.htm

As to your question regarding hollow fruits...this is oftentimes a result of the species (of which there are many). Some species only produce hollow fruits while others produce fruit with edible seeds and some pulp inside. Apparently, you have one of the hollow-producing fruit varieties.

You will want to water it about once a month when it is dormancy. It needs very little water in dormancy but it does need a little.