Probley have 30,000, to 40,000 if I had my achivements from before live.
One game that I did have everything on my old account was oblivion loged in like 5,000 plus hour for sure it might be alot higher than that like in the tens of thousands of hours. I was pretty much the only game I played alot before live so I know almost every thing on the game.
I do have alot more games that are story completed but as for online they are down so never going to happen.
I say getting every achievement in story mode is completing at least for me some online ones are just insane on requirements especailly if they get you kicked.