Ok, thanks! I hope I'll get used to it (or I'll just change the shortcuts).

I just tried xdotool on my laptop but unfortunately this is no option because multiple mouse button clicks block each other. So simulating one by executing another doesn't work.
In the meantime I also found out about the built-in hold-for-right-click feature which is an almost perfect alternative combined with roxterms menu-based copy&paste.

That only leaves the lighter image question open.