1. I am not familiar with Orange Nugget. Did the package list a width? Any reputable seller would list that
2. Short to medium dahlias are fine in pots. But might still need staking. Again, because I am not familiar with this dahlia I cannot say what size pot. Minimum of 5 gallon. You will just have to experiment. When I grow in pots and it is end of season I just cut the foliage off at soil level and put the whole pot in storage
3. Yes they will do well planted among those as long as you have plenty of space in between those perennials. If there is not enough space you may damage the roots of your perennials when you dig them up. But if you are leaving in ground no worries.
4. Yes, but again allow for plenty of space on between plants
A great deal of gardening is just trial and error. All the word guidance in the world is no substitute for seeing how it actually works out in YOUR garden.
