The PMCC Matrix room has a voice system in place to prevent spam. Here's what you need to know:
A user must have voice status to send messages in #pmcc:matrix.org. If you're not voiced, you'll receive a permission error when you attempt to talk.
Ask someone in the room to vouch for you (preferably someone who was talking recently). If they have voice and believe you're not a spammer, you should get a message from a moderator shortly telling you that you now have voice.
If there's no response to your initial request after a bit of time, feel free to message a couple more people or someone talking right then. We won't hold it against you if you don't want to wait a week to say something.
Do whatever you feel is necessary to confirm they're not a spammer (which really shouldn't be much; we don't expect a kind of Spanish Inquisition) and then message a mod about it. All you have to say is that they seem alright and give their username (viewable in Vector web by clicking on their nick on the right in the message they sent you, they follow the form @user:example.com). If you care to say more about your impressions, feel free, but it's neither required nor expected.
Nothing much. Assuming you're fine yourself, people make mistakes. Mods will only start getting worried if there's a long-term pattern of bad recommendations and probably odd habits in chat. You're also always free to message a mod with your questions if you have any.
Good question! Why, yes we do. :) You can see a history of endorsements, voicing, bans, and other moderation events at #pmcclog:matrix.org. Be aware that only mods can talk there, so you'll have to ask in the main room or message a mod directly if you have a question.