Just to clarify, if you are two developers you will need two studio licenses as well. This is in addition to your planned one unattended and one non-production robot.
Non-production robots are very similar to Unattended robots, but are deemed to be used in production-like environments. When you develop a project in a studio and later publish it to Orchestrator, you can choose the robot user and assign the user a non-production license and select on which machine-template the robot will run.
Yes, if you have the applications installed and the robot has access to the required folders (if you have any file-shares the robot uses) then you are good to go. Windows 10 and Windows server will work fine with UiPath unattended robots.
I believe so, your region will have UiPath representatives who also have expertise in helping you with the infrastructure side of things.
The hardest part of the entire process of enterprise / on-premises UiPath is setting up the infrastructure. It is quite technical with all the requirements for certificates, IIS setup and domain names etc. So you would definitely want to have your IT team to help you understand the jargons in the Installation Documentation.
Once you have successfully set up an On-Premises Orchestrator, 95% of your work is done! Allocating licenses is going to be a cake walk
Hope this helps answer some of your questions.