IHS and BRP card

Hi,

I have received my entry clearance which is valid from 21-04-2015 to 21-01-2018,
date of application was 04-03-2015 in Bangalore.
when i had applied there was no BRP or IHS on the application form. I read that IHS is valid on application after 06 April 2015, Is it only for application made after 06 April 2015 or visa stamped before 6 April? Do I need to pay the IHS ?
Do I need to apply for the BRP card ?
Is it mandatory to have a BRP card ?

I am applying for my daughters Visa next week, but I am planning to travel to UK by mid of this month.What documents are required at the immigration ?
I would be submitting the same documents I used for my Visa for my daughter.
Do you think there would be problems arising because of this ?

regards
Sherb