According to my registration date on the Reaper forums I've been using Reaper since 2008, initially running in Windows, running in assorted Linux distros for the last decade or so.
The pun in this post's title is disgracefully clunky but, despite the frustrations and its idiosyncrasies, Reaper has become something of a friend.
It definitely makes me grin, especially when I'm reminded of the nonsense that people who use other DAWs have to deal with.
To be honest, when I tried using it forever ago I got lost and gave up. I forced myself to use it because I liked the feature set, but moving over from FL was very difficult for me.
It took time, but I've figured it out enough to where I can't imagine using anything else.
Any tips for a beginner? I do like some stuff. But I mainly struggle with navigating so many menus and submenus. Being a Linux user and a minimalist at that. I usually try and stay away from using the mouse.
Reaper is very menu heavy, but has a good amount of keys bound to actions. Check the key bindings list and try to memorize them, much like you probably have done for other things given your setup.