Metadata

"Can emails be forwarded to a .pst file and still contain the original metadata."
Yes.
The metadata is embedded in every file you make, receive or send.
Metadata is how your government tracks all your digital correspondence.  
You do not need a third party app.

If you forward it, then you lose the metadata.

If you copy it, then you will retain it.

You can also save it in MSG and catalog it.

Have a look at the Email metadata that you can extract.

For the gmail data, you should probably download it into Outlook.

pst would work, as that will have the header and other metadata too - but of course that is (relatively) hard to read and work with.

Another solution would be to use Thunderbird, which will store the mails (with metadata) in MBox format, and further, can be used to pull data from exchange, gmail etc via imaps, mbox format is essentially just the "raw" mails written (with all headers and other metadata intact) sequentially into a text file.