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This depends on the type of perennial you are growing. Some flowering plants only bloom once in the season while others will continue to put out blooms once the dead ones are removed.

Possibly a bog garden. check out this article: https://www.gardeningknowhow.com/special/spaces/designing-bog-gardens.htm

Another alternative might be a Corkscrew Willow. You could add some hosta and ferns.

Most of your spring flowers, especially bulbs, are considered hardy and accustomed to these conditions. Although they sometimes pop up early under mild winter conditions, there's usually no need to worry if temps drop again. However, if the temperature drops and it makes you feel more at ease, you can cover them with a blanket at night but remove it during the day.

While many people prefer to clean up their gardens in the fall, others prefer to do so in spring. This is usually based on preference as well as your regional climate. I would say in your area, leaving some fall leaves in the beds overwinter would be a good idea, as it not only provides insulation during cold periods, but also will eventually break down in the soil.

Also, leaving growth on some of your plants may help with their continued survival over winter. All dead plants (like annuals) can be cleaned up and disposed of. Spring is often the best time for pruning chores (for most plants) but in warm areas can be done in fall as well. Here is an article that you may find helpful: https://www.gardeningknowhow.com/garden-how-to/projects/fall-garden-clean-up.htm

This should help you plant your year round flower beds: https://www.gardeningknowhow.com/special/spaces/designing-four-season-gardens.htm

When you plan your garden, be sure to consider your USDA planting zone: https://www.gardeningknowhow.com/planting-zones/usda-planting-zone-map.htm