I'm not aware of any addon doing this already.
The naming and reticle stuff, using a title, should work. The title stuff basically is was LibCustomTitles does already, so just make sure you do not overwrite the title this lib uses, as it also is used for RP afaik.
But an icon over the head wouldn't be possible, only if you are grouped, as the position api only is available in groups. If one is still not able to change the nameplates and maybe add an icon in there, you won't have success with this
