It is made clear to new members in respect to their first post and messaging. I did a test account to check. I was not able to send a message to the new account. I am assuming that anyone who already has a PM thread can still reply but, I can't confirm this. The last screenshot is after trying to start a PM.
As far as the first post being hidden until approved, It will have to stay this way. We get a lot of spammers with links to porn ect... About 4 years ago, bots started 1000's of threads in Chinese language. 2 of us couldn't ban the id's fast enough. I'm here 3 times a day during the week, and twice a day on weekends. People don't have to wait too long.