You could prune those blackberry varieties to keep them at 3x3 feet, you would get enough berries for fresh eating, not much more as those plants usually get larger. Once you are getting 3 or so fruiting canes per year per container, you would get the quantities you want. Would not recommend setting on deck during fruiting, it will get stained. I'm not sure what a rubberized plastic planter is. Any container would have to have several bottom holes and the planting soil should be on the coarse side for drainage, and this will require frequent watering during fruit season, whereas plants in the ground would need less frequent water. Your choice of the upright varieties for container planting is a good idea, the trailing or semi-erect varieties will not stay in bounds in a container.

What I would do is remove it from its present pot. Cut about an inch around the root/soil (pot shaped), then cut an inch off the bottom. I would take a five gallon black pot and drill many half inch holes in the sides but not in the bottom. Replant the plumeria in the five gallon pot. Then sink the pot in the ground or sink a seven gallon that is the same height as the five gallon in the ground and plant the five in the middle with soil mix around. At the end of the season, use a key hole saw to saw around the outside of the five gallon and remove for winter storage. If using the seven gallon, empty the soil and cut roots before replanting next season. If in the ground you may want to dig up the roots and soil every few years. You can just plant in the ground and then dig up and bare root store in the winter but this involves cleaning the root ball or handling the mess. I do not think a plumie can make it through the winter in NC as they cannot take any freezing temps.

Congratulations! I know they appear to be house plants but roses are NEVER house plants. They always prefer to be outside in the ground where they will be the happiest. You can keep them potted, in a large enough pot, but they still will need to go outside as soon as the weather permits. For now, if you can't take them outside yet, keep them in as much light as possible and keep them evenly moist but not soggy. It's OK to let the top of the soil dry out a bit in between waterings. Most times people kill these plants by over watering them. They like high humidity but not wet feet. If you have a saucer under them remove them. Then find a deeper dish and put pebbles in it. Add water to just below the tops of the pebbles and then place the pot on top of the pebble but be sure that the water is not touching the bottom of the pot. This will bring up the humidity around the roses without over watering them. Hopefully you can keep them going this way until the weather warms up enough to get them outside.

I have that Tatung unit, and a magnet test doesn't tell the whole story. Some items that a magnet sticks to (my Cuisinart skillet, for example) don't work worth a hoot on the induction hob. Three groups of items that DO work well: my Kuhn Rikon pressure cooker, Fagor pots, and cast iron (both raw and enamel coated). I've found that if a website states that the pots work on induction, you're good to go; I wouldn't trust just the magnet test. I know you have problems with cast iron, so you might consider this: Consumer Reports recently spoke highly of Costco's Kirkland stainless pots, and at least one reviewer has said it works great on induction. I haven't tried any of them, though.