EDIT: i just tried it again, and got into the wasteland with no problems. i was able to walk outside, no CTDs :S. To double check, i fast traveled to springvale and back again and went into Megaton and back out. No problems. I'm not sure what changed, but it seems to be working now. I will report back if it happens again.
Good. I will try to explain some things to you, as I understand them.
1. When you walk around, you periodically hear "Puff" sound. This mean that group of creatures was spawned nearby.
2. If some creature have wrong model (or something another, I'm not sure in this), your game will crash immediatelly, as soon as this creature (or her dead body) will cross your site of look.
3. The best way to fix this issue is to load previous save, before this "Puff" sound. In this case spawn will occur with another set of creatures, and there is big chance of wrong creature missing ,so you will be able to advance further.
4. If you miss this moment, spawn with broken creature already occur and you simply miss this creature, this creature will be still around forever and at any moment can crash your game, as soon as you will look on her.
5. The only ways to fix this are
-to uninstall and reinstall MMM
-To kill this creature with help of KillAll command, or with help of your companions, if they will be able to catch this creature before you. And then wait 4 days interior, for example- in the Megaton house.
I recommend to you CASM mod, which allow to create many saves automatically in the different slots. But don't use Quick load feature from this mod, latest fallout patches broke something. Load your game from game menu instead.
That's all, hope it will help.