faction hits
 

its 1 kill is +1 faction hit how many neg hits for 1 bad faction kill

Totally dependent on the scenario. Usually bad hits are bigger but how big is a case-by-case basis.

Example 1, I routinely kill Kizdean Gix for shits and giggles on a character due to past interactions (IE: Me and this mob have a longstanding disagreement). Despite doing this many times over, faction on that character started apprehensive and remains apprehensive.

Example 2, Plane of Growth. Can't test this yet for obvious reasons, but it was well known that killing only one mob in PoG would cause you SERIOUS faction loss (In my case it was from amiable to dubious). A second kill would nearly always mean you were now KoS.

Completely dependent on the settings of individual mobs and factions.

Typically you lose faction much quicker than you gain it.