Hi Gary,
Main difference relies on the flexibility of the new licensing model to be deployed on any available environment without worrying about cost difference.
The new licenses are called “Flex” License due to it can be setup either on Automation Cloud, Automation Suite, or On-Premise without having to worry about price changes.
Also, how i see it is any license that you purchase will be able to connect to a UiPath Orchestrator Service without having to worry if you will be buying an Orchestrator license. This is because any license purchased will come with a UiPath Orchestrator Service. It just depends on whether you want it hosted via UiPath Automation Cloud, Automation Suite, or On-Premise.
The old licensing model, you have different license options and you have to think of whether you need to buy UiPath Orchestrator as well. If you buy an automation developer, that is it, you have an automation developer. In the event you want to have a UuPath Orchestrator, then you need to buy a UiPath Orchestrator License (Non-Prod). I hope this clarifies.
1st one will include UiPath Orchestrator even if you want it or not, it does not matter if you are not going to use it. You will be able to have access to it.
2nd one, you need to consider. If you need it, then you have to buy it. If not, then you dont need to buy any.
Please refer to the licensing guide for more information. Feel free to ask me if there are other questions.
https://licensing.uipath.com/
For your 2nd point, note, this is my opinion only and not given by UiPath.
New Licensing:
Development Environment - UiPath - Flex - Automation Developer - Named User
Non Production Environment - UiPath Flex - Unattended Robot - Non Production
Production - UiPath - Flex - Unattended Robot, UiPath - Flex - Attended - Named User
Again, the license types I listed here are based on licensing.uipath.com and is only for basic RPA implementation.
There are many more licenses available depending on the services that you would want to consume. As for the quantity, it depends on how many you require. I leave that up to you. I believe there is a minumum number of licenses required. This is something your vendor would be able to cover 
Hope this helps!
Sean