Hi Rick and welcome, Good luck with selling stock I think you'll have fun.
I'd suggest submitting to as many sites as you can within your timeframe, different people sell more on some sites than others depending on their style, it's just finding which ones!
Re the clipping path thing, IMO if you can do it well then yes it will help with your downloads, however SS doesn't support them, iS will check them in Photoshop so it must be good, I've got quite a few on IS with paths, I haven't tried the same image thing you've suggested although I do have the same subject albeit at different angles, the one with the path beats the other one hands down.
Like I said though it must be a good path, if you can't use the pen tool I'd say don't bother.
I belong to a designers forum and posted a question about whether or not they look for images with paths as a prference, the overall opinion is it's the subject that they care the most about, if it has a clipping path all the better.
Hope this helps.

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Richard