Im not sure, but i think, that you can export images with metadata (ratings, keywords, etc.)
The problem is, that Lightroom does not write the data into the file, but only links it with the file via the database. So if you want the data merged with your file, you can tell Lightroom to export this data.
I just had a look and I found at least two options (under "Metadata" in the Library Module)
one reads "export keywords" the other " export xmp metadata to file"
Maybe those two can solve one of your problems.
EDIT: Maybe you can fasten the preview by choosing a lower Preview Quality. You cab change this setting under "Edit"-"Preferences..."-"File Management"