2. In regards of your specific question, once the site has been used in AdWords, it gets its history which is applied to any account.
This means that new account won't matter if you use same site that has already been slapped in some other account.
3. Go back to 1., and you'll figure that submitting a low QS site again in a new account, or submitting same site under different URL is very undesirable today.
To add about new sites (or URLs), I find that young sites have very tough time in AdWords. I believe the best is to earn good history (read Trust) like when you're launching a new site and work hard to get it rank well in organic search.
I also believe that even young site may be welcomed by AdWords - if you have something that other don't - and if it's useful to users.
No strict rule... common sense helps a lot sometimes.
Agree. Get informed.There's a reason your QS is low. Find out and fix it.
I tend to agree as well. There is a ton of information on the subject in the AdWords Help Center and AdWords Learning Center - and the more you know, the better you will do with AdWords. ;)
A good place to start might be here:
Quality Score and First Page Bid Estimates
[adwords.google.com...]
AWA