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Kindle Fire? Another option is picking up a second hand Nexus 7 (2012 or preferably 2013 model) - it'll run Android 5.1 fine.
Regarding photo RSS apps - don't know any good ones. A quick google leads to this: https://play.google.com/store/apps/details?id=info.isaksson.rssphotoshow&hl=en . Let me know if you can't find anything you like - this is pretty to make.