Q1- Does Adsense Ban your account or website if your website is down over 48 hours ?
Answer-No, Google won't disable your AdSense account because your site is down.
It will take time for the AdSense crawler to revisit your site once it goes back up.
Q2- what can I do for accidental click?
Answer-As long as it was a one off and your account is in good standing there's no need too fret too much. Google state:
"Although publishers are not permitted to click on their own ads for any reason, we do understand that accidental clicks may occur. We therefore don't require that you contact us every time you click on your ads. Rest assured that your account is being properly credited for all clicks and impressions we consider to be valid."
Q3-Do I need a Gmail Account to use Adsense on Youtube?
I don't think you would need one, but this is the adsense for websites area. Your best bet would be to ask in the youtube partnership forum.
I "think" that it's more of a preference to Google if you have a Gmail account. I signed up my adsense under a normal email account, but I rolled it into a Gmail account later over my adsense time meaning I can log in with both my regular email and my Google gmail email account into the same account.
Ask here I am just assuming.
http://www.google.com/support/ forum/p/youtube/label?lid= 4c9ae590b9d4fb92&hl=en
I "think" that it's more of a preference to Google if you have a Gmail account. I signed up my adsense under a normal email account, but I rolled it into a Gmail account later over my adsense time meaning I can log in with both my regular email and my Google gmail email account into the same account.
Ask here I am just assuming.
http://www.google.com/support/