When do I fertilize tulips? What do I use?
You can fertilize tulips in the spring. Typically a fertilizer with higher phosphorous is good. Bone meal has a good amount of phosphorous.
Last winter, I planted tulip bulbs. They are growing nicely with big flowers. Should I remove the bulbs from the ground, store them in a refrigerator and replant them during the coming winter in the ground? If so, when I should remove them from the ground and how are they stored?
The following articles should be of some help to you:
To have a garden blooming both in spring and summer, can I plant summer flowers that bloom in July/August on top of the tulip bulbs that bloom in the spring? Can I still plant tulip bulbs now in late spring? Or should I wait until fall? I live in Pittsburgh, PA.
Yes, you can plant your bulbs in succession for seasonal bloom. Here is an article or two that you may find helpful: https://www.gardeningknowhow.com/ornamental/bulbs/bgen/tips-for-adding-bulbs-to-your-flower-garden.htm
How many tulip bulbs can I put in one single hole about 5-6 inches deep and about 6-7 inches round?
I would put about 4-5 bulbs per hole. This article will help with planting tulips: https://www.gardeningknowhow.com/ornamental/bulbs/tulips/tulips-care-and-tulip-planting-tips.htm
Tulips have bloomed, however, remodeling job required digging up plants this week. The leaves had 'drooped' but were not yet yellow or brown. Do I replant the bulbs now or wait until fall?
I would replant them now. Here is an article that will help you so you can continue to get them to bloom:
I was given free bulbs from a friend who pulled the plants up after their blooms were gone. There are still green leaves on the plants and the original bulbs have been divided into 4-5 smaller bulbs. I want to replant them for blooms next spring. I know I should leave the leaves on until withered and dry, but the divided bulbs I'm not sure about. Should I divide them into the several small ones? Are some of these more likely to bloom next year, and if so, which ones are best for replanting?
Leave the foliage on regardless. These articles will help with planting them so they will bloom: https://www.gardeningknowhow.com/ornamental/bulbs/tulips/dividing-tulip-bulbs.htm
I live in Zone 5 and have just dug up mega tulip and daffodil bulbs. They had to be dug up, as the land is going to be all dug up in June. When should these be replanted? Can I dry them and plant them in the fall, or must I plant them now? I certainly don't want them to go to waste.
If they still have green leaves, I would replant them now. After the green leaves are gone, you can dig them up (if you still want to) to dry them out and replant them in the fall.