Once exposed, it is hard to get all pictures online removed or scrubbed. Specially on tumblr if you happen to get reblogged a number of times then even if the original is deleted the pictures remain on the other tumblr blogs.
Even destroyable.io is not "safe". Apparently there is some archiving site that copies all pictures posted and keeps them forever. (undestroyed.xyz).
If you were tagged or named in a tumblr post, Google indexes your name and hence a simple Google search will reveal those pictures. This is impossible to change unless you go through a complex process with Google to "forget" you. Which in itself would be a pretty humiliating experience as you would have to prove that you are that person before they would scrub the search results.
Kinktalk is relatively safe as the albums don't get indexed by Google and you can delete the images.
As to how not to chicken out: find somebody to expose you and send them all your pictures at once. Then, have them expose them one by one. This is what I am doing with my current exposure boi-slut and I know he anxiously checks if I have posted any more pictures, based on how many comments his album has gotten. (Of course, if he really begged me I would remove the album, but I know he gets so turned on by the exposure that he won't!).