Well, Telegram already have a preview feature for every public channels. Just copy the direct link to the channel and add /s after t.me/ (or choose "Previous channel" without opening the link in Telegram) and you're good to go. If only Pavel will add an RSS feed to that feed. That would be mighty-mighty awesome!
More work to save the media files, though. You have to inspect the element and get the direct link to the image through background-image for the tgme_widget_message_photo_wrap class. Much easier and takes less time to just save it inside Telegram, as of now.