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Blueberry bushes generally live 15-20 years. It may be that your blueberries are dying of old age. You may be able to revive them for a time by thinning out the dead branches. It may also be a fungus. Treat the plant with a fungicide to take care of any potential fungi that may be affecting the plant.

Since there are many reasons for this and I cannot see for myself, here is a site that you may find helpful: http://www.fruit.cornell.edu/berrytool/blueberry/leaves/BBmgdef.htm

No, you don't have to, but some people choose to do so only so that the plant focuses its energy on leaf and root growth during the first year or two. It's really a personal choice. If you leave them, it is likely you will see some fruiting this year and, if not, definitely by next year. They reach full maturity by year 3 or 4 and you will see far more fruit on the plant than you did the first 2 years.

You can, but make sure that it does not contain any nitrates. This article will help with fertilizing blueberries: https://www.gardeningknowhow.com/edible/fruits/blueberries/blueberry-fertilizer.htm

This article should help with that: https://www.gardeningknowhow.com/edible/fruits/blueberries/blueberry-plant-pruning.htm

This is a highly debated subject and pretty much depends on the soil, region, and plants. Pine needles are naturally acidic in nature. As they decompose, which is a slow process, additional acid is added to the soil. However, this may not necessarily be a dramatic increase. Since pine needles are acidic, it goes without saying that acid-loving plants (like blueberries, etc.) thrive with this type of mulch. While spruce is also acidic, though perhaps not as much, you could in fact use this as a substitution for pine. However, I wouldn't rely so heavily on this alone to acidfy the soil. I would first have the soil tested, which will let you know how acidic the soil may already be (or not), and then go from there. This article has information on other ways to raise the acidity in soil: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/raise-acid-level-soil.htm This article may help as well: https://www.gardeningknowhow.com/edible/fruits/blueberries/lower-soil-ph-blueberries.htm