What I basically do is import first into Classic, and optionally sync smart previews to the cloud if I want to work on the images on an iDevice as well as in Classic. I then process the images, adding all my metadata (keywords, location, title, caption etc.), then when I'm done I save to XMP, then remove the images from Classic (making sure not to delete the images of course!), then import them to LRCC. That uploads the originals (thus with the metadata) and downloads them back into the Classic catalog.
Of course that only works if you use a date-based folder scheme, so if you're not happy with that the alternative approach (which also works for existing Classic images) would be to import into Classic, then process to complete the metadata entry (edits can obviously be done at any time as they will sync), then write to XMP, then sync smart previews (thus getting the metadata into LRCC), then import the same images into LRCC. That should recognise that smart previews already exist so it will go ahead and upload the originals to replace the smart previews. Because the images have already been marked as synced in Classic, there's no impact there (Classic is made aware that originals now exist in the cloud but they are not downloaded back into Classic as duplicates).
I basically have used both methods, the first method now for all new imports, the other method was used to get existing Classic images into the cloud as originals. Once you have the workflow sorted out it's not too bad (though not for the faint-hearted), but it's a significant workflow overhead that I doubt I would use if I was a professional (or just a more frequent shooter).