herepax183
The Moodle program running in MoodleBox is just an off-the-shelf Moodle from https://download.moodle.org/. So the short answer to all your questions is, "just like in Moodle". They have a big, helpful community at https://moodle.org/.
A longer answer would be: The Moodle HQ maintains a database of third-party plugins at https://moodle.org/plugins/ and you can install all of them in your Moodle(Box) by visiting Site administration > Plugins > Install plugins. There is a built-in version check which will block installing wrong versions (through the GUI).
Trouble shooting is a different matter. Third-party is third-party - there are over 2000 third-party plug-ins belonging to dozens of categories (types). There is no single-sentence answer to that question. The general answer is, "in their respective forums". Some have forums on moodle.org, some are guests in moodle.org forums, some communicate on the plug-in database site itself - there is a message section down below on the plug-in page, some respond in the ticket system of their GitHub page and there are also missing ones! So better, without worrying about a future with 2000+ plug-ins, start with the core Moolde (it is itself a plug-in architecture, many core tools are plug-ins) as it is in MoodleBox. Then with the need, evaluate plug-ins one-by-one and decide individually. Talking of evaluation, MoodleBox is also ideally suited as a test server! Well, if your MoodleBox is in production, buying another Raspberry Pi and an SD card is affordable - in the West at least. Note that you don't always need the latest, most powerful R Pi, even the models 3 B and B+ are well-suited.