You can with the business rule, and I would make them After business rules. You want to create them once the state changes. You can also create multiple demand tasks. You would just have to code it. I don't have any saved to share... it's been a while since I used this method.
For the flow designer, YES, you can. You can even set up creating a task to happen only when the task above it is complete. All you have to do is add the create task action after the 1st one.
The trigger can be tricky. You will have to read each one of the explanations to see which one fits your need.
I usually use an updated one when I know something will change, like your example of the state. But if I need to create something when some are created ONLY, I will add the create trigger.
There are some good videos on the doc that help explain it, and there is some training to help with flow designer
as far as combining two fields, you can try to use the script option for that field
I hope that helps you out.
