1. You have 199 game folders in Saves? The game chooser screen can only read a limited number of those, after about 50 (seems to be around 70 for some players) it just ignores the rest. Moving all but a small number out of the live game folder will cause the startup procedure to use less resources yes, but only a little.
2. Removing the contents of DCBackup is fine (not the entire folder). If you do not leave one small file in there, it's ccmerged.package, then none of your EA Store premium content items will work. The rest of it is there so that if you export sims or lots out of your game to upload or for others to use, and if you had CC on them, the CC would "stick" to the exports. If you never do this, then the folder can stay empty except for that one required file.
3. Error 12 is an out of resources condition. Usually it's memory (RAM), but it can be video memory as well. We covered this just recently and you found that your one ongoing game at the time was fine on RAM usage, well below 3 GB (the danger zone is up around 3.5 GB) both at startup and after many hours of play, but then concluded that there was a lot you were designing that was just too much or too much all at once for the game to handle.
http://forums.thesims.com/en_US/discussion/931820/game-crashing-error-12-code
So same routine, how much RAM is the game using on startup, how much after some play has happened, does this happen in all worlds or just one ongoing save in particular? And note that I listed out many ways to reduce stress on the game in that same post.