if you wanna to create many characters for background use, create each extreme variation, and then deform the character to have mixes of the variations (I did this with morph targets before, and I have done it in maya/zbrush, its a very useful technique), techniques to generate many characters are interesting but they become generic and lack personality (now why making them instead of just buying, and deforming, because you have freedom with texture size, polycount, style, animation, props, and for that reason they can be part of a more unique world but yes they will still be more generic probably a reflex of how they are made), but if you wanna make some character truly awesome make it from scratch usually thats how main (awesome) and important characters are made.
exemple: took a year to develop Altair the main and first character for assassin’s creed (this including lots of concepts and many tests), but for the background characters and less important ones they took from 1 day to 7 days.
*of course this example is extreme usually main characters don’t take that long (it probably took longer because they knew it would be a serie) but anyway they do get more love, and only the best artists get to work on them.
Here some softwares you should consider and games related to the software.
3ds max : gears of war, assassins creed… blizzard games.
maya: uncharted, and there are others but maya is mostly used for animation (many game studios have max for modeling and maya for animation) and its widely used in movies.
softimage: metal gear solid 4, devil may cry, I know people from blizzard who uses it for cinematic modeling, and its also my favorite software, but its being discontinued so Im avoiding it.
modo: Valve games, Wolfenstein: The New order, and others… also its used in movies, and its the one I’m using right now, its my new favorite. (cheaper than maya, and 3ds max… does the same stuff).
blender: its a free software, and i know people who does great on it, but I used it too little to talk about (2 months experience)
them there are softwares that are super important to sculpt, create detail, and realism, those are used together with any off the ones on top:
zbrush: used to create high res models and extract the details, really fun software to work I really have fun sculpting on this one, and I highly recommend learning it, almost all studios (games and movies) use it.
mudbox: its the same as zbrush, and by autodesk(same creators of maya and 3ds max) this software has some advantages to zbrush but its more technical than artistic, its also really fun to use recommend trying.
Sculptris: free… similar to zbrush, and fun to use (its own by pixologic the creator of zbrush)
All these softwares have good, and bad so it becomes a matter of personal preference try them, and pick the ones you like. besides its not important the one you use if you learn one its really easy to switch when need I say this because I have done that plenty of times.
here is my workflow for reference:
concept in photoshop-- model base in modo – detail/highres in zbrush – texture in zbrush --retopology in modo,zbrush,3d coat or topogun – UV in modo – project back details in zbrush – retouch texture in photoshop – rig and animate in maya – have fun in Unreal 4
*some times if the model allow I just do everything but animation in zbrush.
**workflow varies from project to project and from model to model, also from artist to artist
if your area of interest is “high quality 3D character” them there is no other way than creating your own its hard will take time (years) but if you truly like it, will be a really fun journey