Remember when everyone got annoyed with PM SPAM?
In practice resolutions always up being "all or nothing ", especially when issues develop. An aside: I do believe that brand new members really can't upload anything which is good thing. You may typically only have to choose for whatever options are available. You can't at a whim say, after at least one post with a delay of 24 hours before the option is enabled.
Your "stuck" with what the software provides.
You can't arbitrarily have an option in the conversations for everybody that says "User accepts attachments" that is initially off. Even if you had such an option, you inevitably would never find out until you send, which is also annoying. That, sort of, behavior would keep the spamability pretty low.
I would hope, that having PM privs would at least be delayed 24 hours after registering or after having >1 post. PM ing of moderators should always be permitted.