It's nice that the readme links to an example :) I've come across countless github projects for something that seems cool, but don't have any links or screenshots of it in action.
I wrote my (phd) thesis recently, which mean I got to do a survey of the various templates for that purpose.
KOMAscripts wins, hands down. This is cute, but KOMAscript is just ridiculously featureful and customizable. It's also very well documented, can be adapted to any page format and has very good typography.
Nice and clean! I wonder if it requires a lot of tweaking to make it work with letter (it might be as trivial as changing ``paper=a4'' in the cls.) If so, it might be worth the author's time to generalize it.
For the record, another simple and elegant LaTeX template for thesis is: http://cleanthesis.der-ric.de/
I like it this way. My bachelor thesis also had no real guidelines. I frankendopted a thesis template from the Oxford University. It was ok. The biggest problem was it had already used too many latex options, so that I had to go through everything and disable what I did not understand and then make it look good again just to adjust a few settings. But else it was ok. So a new minimalist version is the perfect starting point.
You might try mathtools in place of amsmath. It is a wrapper that fixes some things, and adds lots of useful stuff.
While this is a nice work, it's unlikely to be applicable for its target audience.
in the US at least, individual (universities, schools, departments, degrees) have pre-existing Officially Sanctioned Templates For Theses, and normally failure to comply with them means your document isn't going to be accepted until it's reformatted.
For example, one of my degrees was awarded in 2016, and the version history of the thesis template I used goes back to about 1988, complete with commented out lists of contributors and notes to future generations.