1 & 2
http://www.hmrc.gov.uk/incometax/index.htm

http://www.listentotaxman.com/index.php



Net wage = £3,350 per month

To claim for married allowance, the couple has to be living together.

tax calculation method:-

0-£31,865 @ 20% = £6,373  -----A
£31,866 to £47,000 = £15,135 @ 40% = £6,054 ----B
A+B = 6373+6054 = £12,427

3.
http://www.expatistan.com/cost-of-living/london

Help yourself for the accommodation cost to your own preference.

4.  
After having been living for 5 years you can apply for a permanent residence permit then 12 months later Naturalisation as a British citizen.

https://www.gov.uk/browse/visas-immigration/work-visas
https://www.gov.uk/browse/citizenship
https://www.gov.uk/becoming-a-british-citizen

There are different ways to become a British citizen. The most common is called ‘naturalisation’.

You can apply for British citizenship by naturalisation if:

    you’re 18 or over
    you’re of sound mind
    you’re of good character
    you’ll continue to live in the UK
    you have met the knowledge of English and life in the UK requirements

You must usually also have:

    lived in the UK for at least the 5 years before the date of your application
    spent no more than 450 days outside the UK during those 5 years
    spent no more than 90 days outside the UK in the last 12 months
    been granted indefinite leave to stay in the UK, ie there’s no specific date that you have to leave
    had indefinite leave to stay in the UK for the last 12 months
    not broken any immigration laws while in the UK