When you decide to go freelance, it will take some time to prepare your portfolio for transfer.
You kept all of your rendered footage? Good. You used PhotoJPEG 95%? Even better. This codec is accepted everywhere I submit my footage to. This means, no additional rendering, no additional work. Other codecs will probably work just as well, I am not sure they will work everywhere. Some agencies have file size limitations, if you footage is close to 30s and full of detail, you might have to compress it a little bit more.
With my portfolio I had to re render one file in a hundred.
You kept all the thumbnails? You'll be needing those only if you decide to work with revostock. At some agencies you can not choose a thumbnail, at others you do it online after uploading your file.
What about your keywords? That is the tricky part. One Young Woman Only does not work exactly well outside iStock. What about Woman, Girl optimized to Women? This will not do any good either. Hopefully you backed your metadata up before optimizing at iStock. If you have, you are pretty much set. If not you need to redo you keywords. Maybe do not start from scratch as I tried to do, which is a bad idea. Just unoptimize it if you know what I mean.
Now it is time to prepare the csv. You create a spreadsheet with Excel or open office Calc (which is Free and works perfectly well) containing all of the metadata in the world. That is file name, file ID, title, description, keywords, model release name, thumbnail name, categories etc. The way I do it is, I keep data for all agencies in one file. Then I export specific agency columns, as a csv file, upload it, and it is done. No deepmeta, no optimizing, no wasting time copying and pasting over and over again. I love the simplicity of this csv solution. With some agencies like shutterstock you will need to adjust the keywords online but it does not take so much time as the entire process at iStock takes. If you need help with the metadata, send me a targoszstock gmail. I have a few files you may find useful.