I suggest Edward Deci's book, Why We Do What We Do. Deci and his colleague, Richard Ryan, are the founders of the current most popular theory of human motivation: Self-determination theory. It's a very short book and extremely easy to read.

I know you're looking mainly for practical stuff and this book is primarily theoretical, but I think you should check it out for two reasons: 

1. It's an easy to understand theory that you can use to assess and update your habits with when they don't work as you planned.
2. Past theories of motivation focus on external/extrinsic motivators, like money, grades, etc. It turns out that these things don't promote intrinsic motivation, and they often undermine it, leading to poor long-term results. It's important to keep this in mind when you're looking for advice to act upon. In the short-term, extrinsic motivators are great, but when they undermine intrinsic motivation, they lead to a kind of boom-bust pattern when people implement new habits.

Deci and Ryan also have a short paper that gives an overview of their theory, but I think the book is much more informative and worth the read.

The Center for Self-Determination Theory has some good (and mostly short) resources too, like this overview of all the mini-theories that make up self-determination theory. 

My friend Rémi Theriault wrote a great blog post for the CPPA Students Medium titled "Time Management: The Importance of Self-Monitoring". Rémi is a psychology PhD student at the Université du Québec à Montréal studying topics related to motivation, self-determination theory, and positive psychology. He's one of the head ambassadors in the student branch of the Canadian Positive Psychology Association. I like Rémi–he's practically-minded, and his practical insights are informed by theoretical and empirical evidence.

I've written an essay for the CPPA Students Medium on strategic reading. It includes tips on being a more effective reader, so if you're looking to increase your reading and writing time, it may help you read more efficiently. I'm also working on an essay for them on self-determination theory, but it won't be released until the Spring (probably mid-March).

Hope this helps!

I suggest Atomic Habits by James Clear. Building a habit effectively is a main topic but I believe that it's closely related to motivation (and there's some content about motivation as well).
I liked the book due to its simplicity, pragmatism and well articulated model of a habits and "levers" that you can use to influence it. I still haven't implemented all of the strategies/ideas from the book but a couple of them continue to have a positive impact. For example adapting/creating your identity so that it reinforces the habit (e.g. thinking about myself as a runner increases the chance that I'll go for a run), and being more focused on my environment and how it supports/weakens new habit (e.g. hiding my tablet in a drawer in a separate room increases the chance that I'll read a book).

I'm not sure how well these meet your criteria, but since you've asked a good question and had no responses I figured that potentially-not-precisely-matching responses might be better than none.

• Willpower literature, e.g. the book by Baumeister and Tierney. (Not sure how much of this has replicated.)
• Getting Things Done, David Allen
• Flow, Mihaly Csikszentmihalyi
• Digital Minimalism or Deep Work by Cal Newport

These are not endorsements of these books, per se, but things that I have come across that I think might speak to your initial 3 questions, although perhaps not that well meeting your 3 criteria listed near the bottom.

Hope they help, and either way, good luck with the project!