Hello there, I'm just gonna suggest remarkable hacks from ddvk on GitHub
It's only for version 2, the 3 breaks things sadly, and they're binary patches, but incredibly usefull. (Downgrade is possible I think)
Also here's a list of many great projects if you'd be interested in hacking your RM a bit more :)
I use Canva to make my templates. Save as PDF and use the Remarkable app to import the new template.
I've been using Linux almost every day since 1993, so SSH isn't "foreign" to me - in fact I've written some of my own scripts to work with the tablets.
With that said, I also paid the $12 for RCU. I can upload custom templates by hand, but RCU makes it so much easier. (And yes, it's a third party program, the developer is a lot more responsive than anybody at reMarkable, and he's been known to read this sub.)
I haven't paid for anything other than RCU itself. I've created my own templates, in fact the original reason I started the remarkable.jms1.info was to share the information about how to make your own templates. Most of the other content came later, and I have a backlog of things I want to write about but haven't had time. One of things is the rm2-cal script, which generates simple but (I think) useful "daily calendar" PDFs, similar to what I've seen other people selling on etsy. (Functionally similar, but not as pretty - I have the artistic talent of a sheet of drywall.)
I made my own application to copy my custom Splash Screens and Templates after every update. I had bought an application for template update and creation but it stopped working. I create my templates in word, custom page sizing. And then use any online converter to convert to .SVG and .PNG.