Must I keep in pot or grow outside?
You are in USDA hardiness zone 7b and bird of paradise plants are only hardy in zones 9-11. They are severely damaged below 24 degrees F. So, it's best if yours is brought inside for the winter. Here is more:
Please, any tips how to chip off plants from a big plant of bird of paradise please
Here you go!
https://www.gardeningknowhow.com/ornamental/flowers/bop/dividing-bird-of-paradise.htm
Happens soon after the flowers open.
The plant may have a severe infection. I can't say which without seeing the damage.
Fungicides will be in order. These articles will help:
https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm
https://www.gardeningknowhow.com/special/organic/biofungicide-information.htm
https://www.gardeningknowhow.com/garden-how-to/info/homemade-fungicide.htm
Replanted them in big black potting bags. Roots now start growing through the bottom of the potting bag into the soil. Must I cut back those roots? About three years old plants.
Here are two articles that will be helpful with your root pruning questions:
https://www.gardeningknowhow.com/houseplants/hpgen/prune-roots.htm
https://www.gardeningknowhow.com/ornamental/flowers/bop/transplanting-birds-of-paradise.htm
MY bird of paradise suffered cold damage. How much can it be cut back ?
You can cut the stems back to the trunk, but do not cut into the trunk, according to the article below. Severe damage may show in dark or black stems and soft spots in the trunk. Give it good care and it may recover. (Generally, when pruning, do not cut more than 25 percent of a plant in one season.)
https://www.gardeningknowhow.com/ornamental/flowers/bop/bird-paradise-plant-freeze.htm
I have several Bird of Paradise which were from 1 plant years ago. I have yet to get a complete bloom. They always seem to rot at the base. I have loads of blooms on my plants right now that are on the back porch, which is closed in. Today my husband put up some grow lights, I thought maybe that would help. But even last year in the yard I didn't get a pretty bloom. Please I need help.
There aren't many diseases that attack this plant, but root rot, and insect problems do crop up from time to time.
With that being said, fungicides and insecticides would be my first trial.
I would look at the soil nutrients and pH also. This being out of balance will cause blooming problems, as well.
Here are some articles that will help:
https://www.gardeningknowhow.com/ornamental/flowers/bop/bird-of-paradise-plant-diseases.htm
https://www.gardeningknowhow.com/ornamental/flowers/bop/bird-of-paradise-plant-bugs.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-soil.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/soil-ph-plants.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-moisture-in-plants.htm
We have one that is very healthy with numerous blooms, but are worried that the secretion from the flower may be harmful, or it to attract the bees etc?
The bird of paradise flower does exude a sap, but the mildly poisonous parts are mostly the fruit and seeds. Ingesting it could cause gastric discomfort.
https://www.aspca.org/pet-care/animal-poison-control/toxic-and-non-toxic-plants/bird-paradise-flower