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I believe the following article addresses your question: https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/hibiscus-leaf-drop.htm

Without a photo we can only guess and generalize.

Branches growing from the main trunk are not necessarily suckers, and may be just natural branching that should be preserved and not removed.

If you mean that there are multiple shoots coming up from the same area at the low point just above the soil level, then those might be considered suckers, and maybe they should be thinned or removed.

Unless you have the tag from where it came from or know who planted it, it may be difficult if not impossible to find the exact cultivar. The only thing that we can pin down is that it is a tropical variety. They are the only type that can flower orange, like this.

Here is an article that will help you with their care: https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/hibiscus-container-care.htm

It sounds like your basement will work fine as far as the temperature goes. The hibiscuses may look a bit rough when they come out in the spring. Here's an article with info for you:
https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/wintering-hibiscus-indoors-winter-care-for-hibiscus.htm

It could be thrips or gall midges inside the buds. These articles tell more and how to control them.

https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/pests-on-hibiscus-plants.htm

https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/hibiscus-flowers-hibiscus-blossoms-falling-off-plant.htm

I have not had success with that. They are tropical plants that require >6 hrs of sun to produce enough food for the roots but they do not hoard enough in winter to survive long, dark winters. Can you try putting it in a south facing window with some light instead?