Is it true I can go back to Vault 101?

If yes then please let me know (with minimum spoilers) what things I need to do to be able to go back and check things out.

And if I aim for multiple targets in V.A.T.S. and the Mysterious Stranger appears will he just kill one targer or does he shoot all that I am locked on?

One last thing, Does having Dogmeat with me lower the rate of the Mysterious Stranger appearing to help me?

Sorry if there is a wiki that covers this but I can't locate it and I think it would be better to get advice from gamers directly.

Yes, you can go back to Vault 101. After a quest called 'The Waters of Life' has been completed (it's during thr MQ), go back to the area near 101 and you'll get a radio signal.

I'm not sure about the second or third question -- I'm ashamed to say I've never used Mysterious Stranger. Though, I don't see why Dogmeat being there would lower your chances of him turning up.

The Mysterious stranger will only kill the person you locked onto. Once he does his job, VATS is over
And about the last question, I dont think so

Yes, there is a wiki. But don't use it! It has ruined the gaming experience of so many people by having explicit spoilers even in the most innocent articles.
On questions:

1) Once. As a general hint, visit Megaton after you have made first contact with the game's villain and look at your list of radio stations.

2) I believe he can appear only once per VATS session, but I'm not entirely sure.

3) No. Dogmeat is a companion just like anyone else. A normal NPC just scripted to follow you under the right circumstances. Mysterious stranger's appearances are handles by completely different scripts.

Cool,
Thanks folks.

Also what I meant on the Mysterious Stranger, (Sorry I should have been clearer) When in VATS, I lock onto lets say 3 raiders and then I fire at all 3 but then 2 die but the Mysterious Stranger appears to kill the last one. So what I was wondering is if I fire on all 3 targets and all 3 live, would the Mysterious Stranger shoot all 3 at the same time?

On the points of the "wikis", That is why I try to avoide those because I hate spoilers unless I hear bad things about a game. I got plenty of time to do Vault 101.

Thanks again :goodjob:

I just noticed this, and I'm curious. I've never seen VATS lock on to more than one target at a time, even when that "target" is a companion or ally who just happens to be closer than my intended target. Can VATS lock on to more than one?

In VATS you can fire at as many targets (in sequence, one after the other) as you have Action Points and ammunition for. But no, it won't highlight more than one at a time- you just have to cycle through them and queue up shots on each in turn.

Look for the arrows on your screen.