I’m still not sure that filter thing is necessary. FreshRSS can fetch content and images using the CSS selector of the website. You may want to check out the Advanced section in their documentation: https://freshrss.github.io/FreshRSS/en/users/04_Subscriptions.html#retrieve-a-truncated-feed-from-within-freshrss
Anyway, whatever works for you :)
I see you have the G502 in your current list: Make sure you get the X variant as those are using optical switches. I believe piper still needs a beta build to have the mouse included.