I have now finished uploading my first fifty images to my initial three sites and have begun sending them to some of the other sites on my list.
Shutterstock continue to be frustratingly picky, with only 29 of 50 accepted (58%). All of these were images which were previously accepted on iStock (where I had an acceptance rate in the high seventies). Probably the most annoying rejections are for 'limited commercial value' when applied to images which have sold well previously and therefore have a proven commercial value.
Something seems to have gone wrong at Dreamstime and all my 50 uploads are stuck in their queue, uninspected. I have sent an email to support and am waiting to hear back.
The only other site worthy of note at the moment is CanStock, who have reviewed all my images very quickly and accepted a very high percentage of them. No sales there yet, or anywhere else either with the continued exception of Shutterstock, where sales have been reasonably brisk. I have also had a couple of non-subscription sales there, which helps a bit. I think I could do well there if I could just get more images accepted.