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While you don’t have to use dwarf hydrangeas in pots, you may want to if your space is limited. Hydrangeas don’t just get tall; they also get bushy. Look for plants specific to your growing zone and size constraints.

https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/hydrangea-container-care.htm

I wouldn't remove any leaves that aren't yellow or brown. A young plant needs all the photosynthesis it can get. I think the blooms are too heavy for this plant that hasn't had enough time to sink in strong roots. If you trim a couple to take inside, the plant may straighten up. A hoop is fine as long as you are very careful not to damage stems. Hydrangeas like moist soil and morning sun unless you have one of the ever-blooming hybrids. Keep your plant tag; how to correctly prune hydrangeas depends on the type you have. It is easy to forget by the time you think about pruning. Here is a link to a number of articles on hydrangea care: https://www.gardeningknowhow.com/search?q=hygrangea%20care

This depends on the variety of Hydrangea.
Many gardeners leave the flower heads for winter interest.
https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/hydrangea-winter-care-how-to-protect-hydrangeas-from-winter-cold-and-wind.htm

The plants below are not Hydrangea, but something that has been self seeded in that area. I am not able to identify it though. I would remove it, you could let one or two mature and maybe identification would be easier if a flower forms.

In areas where temperatures annually stay below freezing for long stretches, hydrangeas die back every winter leaving a mound of dead stems to prune away in spring.
https://www.gardeningknowhow.com/garden-how-to/gardening-by-zone/zone-5/zone-5-hydrangeas.htm

What is your normal feeding routine? These should be fed once per year in early spring for best flowering. An all-purpose will suffice.

Is there an adequate amount of shade? Too much sun can stunt them as well.

This article will give you more information on the care of these shrubs: https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/mophead-hydrangea-care.htm