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Swede, rutabaga and turnips are all pretty much the same so if you are currently experiencing bolting (or going to seed), you could cut the flowers BUT cutting the tops off will not reverse this problem. A Swede turnip gone to seed is fibrous, has a woody taste, and is not suitable to eat. Therefore, it is best to pull up the plant once it bolts or leave it to self-seed, if you have room.

It sounds like what you have is a root maggot problem. There are many species of root maggots so their color may vary from one to another. However, their taste for root crops, like turnips and radishes, is the same. Here is an article that you may find helpful: https://www.gardeningknowhow.com/plant-problems/pests/root-eating-insects-identifying-vegetable-root-maggots-and-root-maggot-control.htm

Yes. Select young, medium-sized rutabagas. Cut off tops, wash and peel. Then cut into cubes and blanch these for about 3 minutes. Allow them to cool, drain and pack, leaving 1/2-inch headspace. Seal and freeze.

Hopefully, this article will help: https://www.gardeningknowhow.com/edible/vegetables/rutabaga/planting-rutabaga.htm
There are related articles listed at the end of the above.

Personally, I've never heard about removing the older leaves to promote growth. You could experiment with a few plants.

This can occur for several reasons. Most likely is that it may be getting too warm too fast for them. They start to bolt before a proper root forms.

It may also be that the soil is too hard. Or there may be a lack of phosphorous in the soil as well.

Have your soil tested and try to plant them during the coolest weather they can tolerate.