If you are the publisher you own the mechanical copyright. Though to make any benefit from it you need further advice about MCPS - but from what you post that is not a big consideration.
The copyright on the non-PD tracks is another matter. The words and music are the copyright of the original composers &/or the copyright holder. And that is the demesne of the dreaded PRS.
Once they know of the CD you will hear from them. But maybe 500 copies is not big enough for them to bother too much ---- maybe. It all depends on marketing & publicity and how they find out. If you get the permission of the copyright holders direct, it may be OK.
I am making DVD's with music on them and I choose tracks from those who I can ask for permissions, but these are not for sale they will go to the contributors, of whom there are many (eg also those in the video/stills)