Making use of Second Mouse Wheel / horizontal mouse wheel (on a gaming mouse) in Premiere Pro

HesusMedia, I have this exact same workflow. My solution was to simply customize my Rat so that ThumScroll is programmed to trigger the keyboard commands for FrameNext and FramePrev (I can't remember what those are off the top of my head... square brackets, comma period?). This takes the customization outside of Premiere into the Rat settings, but nets the desired outcome. I would also recommend adding Cyborg Auto Profiler (Cyborg Auto-Profiler download | SourceForge.net ) to your list of tools (not mine, not affiliated). This allows you to configure multiple profiles, one for each application, and use the auto profiler to automatically switch profiles depending on which program is active. This makes switching between Premiere, AE, and Maya/Blender seamless because even those all use different frame-next/prev keyboard shortcuts, on my computer, my thumbscroll is FrameNext and FramePrev in all of my applications.

scroll the timeline horizontally and use the standard scroll wheel for zooming in, jump single frames, adjust track height and similar things.

You can already do all those things with the default vertical scroll setup.  There's really no need to separate out the timeline scroll.

You would need to probably set up a profile for Premiere in your mouse configuration software that tells your secondary scroll wheel to mimic the shortcut you are using in Premiere for horizontal scrolling.