The answers to your questions, in order: you might qualify for an L-1B but this would depend in part on the nature of your specialized knowledge of the company'

The answers to your questions, in order: you might qualify for an L-1B but this would depend in part on the nature of your specialized knowledge of the company's proprietary products, systems, etc.; underlying status has nothing to do with green card options, the green card requirements are separate and apart but on the face of it, it looks like you would have a solid PERM-based green card application; not necessarily but you would need to stay with this employer for a while, while your green card application is pending, before you could "port" your application to another employer.