Your action plan is already good, but there are a couple of other things you may want to consider.
Firstly, be very transparent about how you are prioritising. Make your approach to the cost/benefit analysis public and share it widely.
This will help when the inevitable questions arise about your priority order.
Secondly, you may want to consider a cull ...
Although I support what Todd wrote, there is more under the surface than above. So my answer based on my experience as a program director is as followe.
The "golden" triangle is a myth (yes its there on an economic/math basis) but we are talking about social systems here.So as Todd pointed out you will have no chance to succeed on the given parameters. ...
Increase Resources or Set Expectations Lower
I'm not sure what your actual question is, because from a project management perspective you have only three core sliders (also known as the "iron triangle") that you can adjust:
What you seem to be talking about is scope management as the adjustable slider, which you can tune to accommodate ...
Since I am simultaneously a project manager and a seasoned software developer, I will comment here:
I also believe that this task might have been assigned to you – as a junior developer – partly to expose you to the differences. They're asking you to familiarize yourself, and then recommend. And the first thing they're going to then smile and ask you is, "...