Welcome aboard!
Read the PBP wiki and poke around and learn how to use the forum.
The rest of this is mostly what I've learned after a decade in open-source as a non-developer. Basically do your best to learn things for yourself before asking others, and develop good research skills since software is a moving target.
As a person new to Linux Kernel based OSes, aka "distros", stick with Manjaro until you are confident. As a new user a lot of your impression of "Linux" will really be the desktop environment and the software available to the operating system supporting the DE. That's your skills grow you will develop preferences. Try to learn how to do things with Manjaro that are done on more popular OSes, you'll learn a considerable amount this way. It is also what the community supports on the PBP, making your introduction to this community easier.
Try not to mess with the hardware like adding an NVME device or switching to SD boot until you are confident with the console/command line/cli/terminal (and whatever other term is used). Learn how to copy files, move them, create them, edit them in the cli. Learn about Linux file system hierarchy and the nuances specific to Arch Manjaro. Check out those projects official forums and homepages.
Learn how Manjaro manages software updates and how to install software through a package manager, or container. From there and you can learn about SSH and trying to SSH into your PBP from whatever OS you are accustomed to. When following tutorials be sure to understand what the actual commands and command flags actually do through the man pages. (man for manual, aka man ls in a cli to understand more about the list command). Well it's convenient to use a gooey based tool, To get the most out of your machine it may be helpful to understand the cli equivalents, that's a lot of graphical utilities and Linux are many other utilities assembled together with a graphical overlay.
There is no one right answer and there is no one"best"whatever in open source, There are a ton of tutorials and articles with top 10 lists and stuff that can be hard to navigate as a newcomer. Try out different resources to find the medium that you learn best with tech whether it's vloggers on YouTube, reading the wiki or technical documentation like "man pages", following developers mailing lists, IRC, tutorials, or whatnot. There are often a lot of strong opinions here do not be intimidated by them. Do your best to try to find out answers for yourself before asking someone else to donate their time, and you will do OK.
Also keep in mind there are different families of Linux OSes that the majority of Linux distros are forked from. And especially with Pine64's offerings and most SBC's the OSs are tweaked in such a way that you have to be very careful about what software and commands that work in the particular environment. The more niche of a project or piece of hardware you use the more likely it is you will have to adopt suggestions or tutorials to fit the goal you were trying to accomplish. For instance I do not use Manjaro so I do not know the specific resources available to that project, however I do often consult the arch project's wiki. Especially The first time I was converting a Debian based server into a desktop workstation, explanation on window managers and desktop environments and the way it was organized was easy to read and very complete on the Arch wiki. Unfortunately since a lot of things on opens source are volunteer based there is a lot of outdated information and you have to be mindful of the source of that information too. Outdated doesn't always mean obsolete though.
Good luck and have fun!