The only book I ever had on Linux was Dr. Linux, a gigantic paperback, and I didn't read all of it.
Mostly, I learned from the man pages, some of which were terrible in the 90s. Thanks to the Debian documentation project, Linux man pages have been better since about 2000, but I think FreeBSD's man pages are much better still. Providing and maintaining the manual pages is taken more seriously, especially for system parts which aren't shell commands. It helps that FreeBSD commands and drivers have more sensible interface design. As a career sysadmin put it: FreeBSD is Linux for grown-ups.
OpenBSD will be somewhat simpler still, and its manual pages are just as good if not better. However, in the last few years, they have started to sacrifice simplicity for security. At one point, someone told me he thought more people use OpenBSD than FreeBSD for desktop systems and thus OpenBSD was better suited for it. This would have been around 2017.
Networking I'm pretty sure you'll find much more straightforward in Free- or OpenBSD than in Linux. However, it's been a long time since I really messed with it.
I learned bash from its man page, but I didn't really get comfortable with the quoting rules. I'm told it's not bad when you understand them. You need to use quotes a lot. (This goes for any Bourne shell.) If sh(1) is readable, try learning from that first as it's a generic Bourne shell reference, omitting Bash's extensions.
Incidently, FreeBSD defaults to the C shell for non-root accounts. I think this is a mistake in modern systems, the C shell being rather clumsy and a little less powerful than bash. It made more sense when there was no Bourne shell with full-featured command-line editing and completion.