ILR - Calculating 5 years continuous period

[VaniVishu]

Hello members

I am a newbie here and will appreciate any advise you can give me regarding my ILR application due in June 2013.

Received Work Permit Visa - 10 June 2008
Entered UK - 30 July 2008
Total absence from UK so far (147 days for reasons of Annual leave, Sickness, Compassionate grounds and maternity leave).
My visa ends on 10 June 2013.

My huge worry is that I lost 50 days between the time Visa was granted and I entered UK. So I will have only spent 4 years, 10 months and 10 days only at the time of applying for ILR. A recent home office document dated 13/12/12 states that period between entry clearance grated and entering UK can be counted towards qualifying period as long as its less than 3 months, should I count this as absence from UK (which means I will have a total of 197 days absence - 147+50)?
The reason for this 50 days lapse is because, my employer was recruiting 10 employees and some of them had a delay in getting their Visa. Since we had to all travel together, I had to wait for 50 days before all of them were issued Visa.
Also, I changed job. The employer is the same, but I have moved departments (from children to adult social care) and my pay had been steadily going up throughout these years and I an currently earning 32200 per annum gross.
My husband has set up a small business here and has invested a lot of money. well, 'lot' by our measures but not enough to apply through entrepreneur route, I am afraid. So its imperative that I should get ILR.

My query is, what are my chances of being granted ILR?
Will my change of job impact the application outcome?
Should I write a covering letter to say why I had to delay entering UK?
Should I apply by premium service or post?
Should I pass Life in UK test or do ESOL course?

Please advise me.
Many thanks