I'd like to recommend the book "trading at the speed of light". It's an in depth look at the world of high frequency trading based on first hand interviews with traders, court documents, etc. It would appear based on what little information is actually available that HFT firms net only modest profits after taxes and fees on trades. Historically, it appears most firms fail to turn a profit and shut down. A paper of Laughlin (2014) suggests virtu, a hft firm that now executes Robinhood orders, earns an estimate profit of 0.24 cents per trade, with 0.05 to 0.1 cents per share traded being a respectable profit.
I highly recommend this book though if your into this topic
This is exactly what PIR is for. A good intro is chapter 6 of the (awesome and ahead-of-its-time) book Malicious Cryptography. One of the authors works at the agency now, I believe.
There's been a lot of work on racketlang adding a gradual typing system. You can write without types, and when youre ready, refine your code by adding types where necessary.
I'd recommend Ben Klemens' excellent book "21st Century C - Tips from the New School" [0]. This book teaches you modern C techniques and, most importantly, the tooling that modern C programmers use (git, autotools, valgrind, etc.) It also covers commonly used libraries to help you from reinventing the wheel (GLib, POSIX standard, SQLite, libxml, & cURL.)
As mentioned in another post, David Hanson's "C Interfaces and Implementations - Techniques for Creating Reusable Software" [1] is a great book, stressing the design of good APIs. This book in particular might help you in your goal to become a better engineer.
On the free side, there's an excellent PDF by Jens Gustedt, "Modern C" [2]. I've not read the whole thing but it seems like an in-depth look at C11.
John Regehr's blog "Embedded in Academia" [3] is a good resource for C programming. You'll learn a lot about weird edge cases and undefined behavior. He also has a recent post about teaching C, with suggestions for resources [4].