How do I translate product requirements into components, schematics, and programming?
How do I know what "things" already exist as components,


Most online electronic component dealers have search engines that will let you browse for components with specs matching your requirements, that is if you don't already know what components to use from years of experience.


  and what are some ways to evaluate those components in terms of suitability?


Depends completely on the components and application in question. Actually I would say that knowing how to choose the right design and the right components, and to know what factor are important to your design, and so on, is the main part of what being an EE is, and I would have thought you should have learned a lot of that through your education.


  How do I know the best way to develop the software needed for my project?


If you had a degree in Software Engineering you would/should have known that, but I would also have thought that you had learned some of that during your degree. If not then you need to study how to develop the software you need, and then you have to work through it, blood sweat and tears, until you get there.

But what really worries me, is that during your degree you didn't learn how to acquire the knowledge you need to solve problems you haven't solved before.