Well there is no easy answer with out having a clue as to the full design of the game in question. Do you need characters that can act as in “The Last of Us” or a fast paced on-line shooter like “Unreal Tournament” as the type of game usually dictates the level of fidelity required.
Do you wish to use morphing on hero models or on NPC alone?
Do you even know that if an object can or can not even be tessellated?
Our general rule #1 though is to build to what it would take to make it look good as it’s far easier to make it less than trying to make not enough do more so if you start with an object that is 20k you can always make it 5k via the addition of LOD’s or old school modeling swapping.
This keeping in mind.
Not all things should be built as to their intended use but also take into consideration other areas of the game design that fidelity does not impact performance or game play. You character or player model set up for example could be a hero version fully loaded with eye candy or as a model swap for QT events.