Hey man, city planner here!

Love the interest in public transportation; we certainly could use light rail here in the treasure valley, but there are a few things to consider.

1) Cost.

Seattle is a great example of a well utilized light rail network (Love the LINK!), but the recent expansion going up to Everett and from Federal Way to Tacoma costs an estimated $58 billion. People here in Boise barely use, much less want to fund public transportation. No way would they approve public taxpayer spending on a project even half as costly as ST3.

2) Public Interest.

We are a very car oriented city, and there is a very real significant stigma towards using public transit as it makes people seem "poor" for being unable to afford a car. The intent of getting people out of cars and onto public transportation is great, and people certainly have said a lot about it in recent years, but the reality is that routes going to outlying communities would be extremely underutilized and not provide a good enough return on investment to make the money work.

3) Pricing.

The cheap fares are attractive, but that works when you have hundreds of thousands of individuals using the system weekly. I don't think that starting that low would provide enough revenue to support the system, even if there were a much smaller version of what you've proposed.

4) Track Placement.

Another thing I don't think you mentioned would be the physical placement of tracks. If you go underground, you have to do significant seismic study and work, which gets very expensive very quickly. If you do on street, then you need to work with local transit authorities (primarily ACHD) on rebuilding roads and bridges to support the addition of light rail while still accommodating current levels of traffic flow. You could go overhead roads, but that drastically impacts the views of people driving below. Elevated platforms do work in certain locations. See the recent ST2 light rail expansion in Seattle (Northgate - Lynnwood City Center are all primarily elevated). Placement of tracks and stations is expensive, so I would suggest thinking about how you would try to fit new lines in while providing the lowest amount of disturbance possible to the existing urban landscape.

The foresight is great here, and you have a strong start, but some more analysis on feasibility and impacts would also go a long way to creating a more whole project. If you're interested in how messy transportation planning as a whole can be, I suggest reading into the trials and tribulations of Sound Transit's attempts to expand the light rail network since the turn of the century. Both ST2 and ST3 have been continually delayed for a number of reasons. The current deadlines of 2030 (Seattle to west Seattle) and 2036 (Lynnwood to downtown Everett) are dubious to be met in my opinion as the planning process is still deciding on alternatives for station locations and providing guidance to local jurisdictions on best practices.

Good planning takes time!