Dierdre,
But I am most concerned with being able to get into LR4 without any mishap...
I want to be able to use the LR4 Cataloguing
Are PM file Names and Keywords compatible LR..
Will LR rename the file?
Will the PM keywords be saved in LR?
I will be using Stars and eventually colors...
If you're using RAW files, make sure you're not embedding IPTC or XMP into them. Adobe's applications work best with a pure XMP sidecar file workflow.
To get color class labels working between the two, you'll have to make sure that the text labels are the same in both applications. I'd just copy them from LR and paste them into the General section of Photo Mechanic's Preferences dialog in the corresponding color slots.
Filenames should be fine. As far as I know LR has no filename restrictions.
Keywords, including hierarchical (we call them Structured Keywords) keywords should be just fine.
Star ratings should just work.
Please note that you will likely have to tell LR to re-read XMP if you have already imported your photos into LR and you later make changes in Photo Mechanic. This is because LR uses a copy of the metadata in its database and doesn't automatically check for external changes. There may be a setting in LR that will make it check for changes, but I don't know if they added such a feature.
HTH,
-Kirk