Not that complicated, posting is very similar to Tapas, just a tiny bit differences in the sizes of files, but nothing that can't be done with CSP or Photoshop.
The series I work for don't care much about having much prep, so we post when we can or when the next episode is finished, we schedule everything so it's posted at the same time on the different websites.
In your case, I either recommend scheduling your series to one episode per week until it catches up to your series on Tapas, when it gets close you simply announce "now the series will release X days" either in the description of the episode or within the credits.
When I self promote I mention the places where you can read the series, some people even have that on promo images or in the credits of the episodes, kind of as a reminder in case someone needs to switch or one of the sites is under maintenance.
Nope, just a simply resizing and done, not that complicated, doesn't take more than a few minutes. I already work on big sizes, so adjusting to the demanded size file and format is not a big problem, if your image size is smaller than the new site's then... it may be a bit complicated or may look a bit pixelated, but people won't notice on most mobile devices, on pc yeah but nowadays not many read on pc... it's either on phones, tablets, ipads or even netbooks