Jokes apart, here is my attempt to "answer" your questions -
1 - What you have will suffice. Though you are not required to submit any evidence of your residency at those addresses
2 - Use the reference number on top right corner of your "first ever visa" be it student or be it T1
3 - Round it up to the nearest date you remember
4 - Well, your earnings can be any of the past 12 months in last 15. Your bank statement can be 1 month old to the day you appear in PEO or post your application. So for example - you can claim from 1/7/2011 - 30/6/2012. Appy on 18th July at PEO or via post and you would need the bank statements and payslips from July 11 to June 12 (Inclusive)
5 - I have covered in above comment
6 - Yes. But your end date would be 30/06/2012 and NOT 1/7/12, I am sure being highly skilled you can work out why !!!
7 - NO - Read carefully, at this point I am struggling to understand how you were qualified for "highly skilled" ??? Anyways, you would enter the amount you earned and not what your yearly salary was !!!! So if your salary was £12,000 per year and you worked there for 6 months, pen down £6000
8 - Covered in above comment
9 - You've got to be kidding me !!! YES IT IS BEFORE TAX !!!!!
10 - YES
11 - YES
I am going for a fag break
hahaha
An [Expensive] Immigrant journey has ended 19/08/2015. Good luck to you all out there...