Always, always, always add your metadata to your original image - I do mine in Photoshop, but wherever your "final" version of the image comes from will do.
First, you only want to do the work once. Given the way each site works, you'll need to tweak things a little at some sites after upload, but the basics don't need to be done again.
You also want that data in the image so that when/if in the future you want to upload to a new site, you don't have to re-think what you did and then do it over, possibly forgetting a useful keyword. Or, where you have to find it at one of the earlier sites and copy/paste your keywords from there (might be fine for one image, but try that for a portfolio of thousands)
And never use terminology specific to a site in your keywords - for example, Getty's controlled vocabulary uses Residental Structure for house or home, and Front or Back Yard for garden or yard