Tier 1 to ILR 5 yrs period calculation with 100 days break

[fusion2014]

Could you please help on Tier 1 (General) to ILR 5 yrs continuous period calculation
Tier 1 visa issued : 8-Aug-2009 to 8-Aug-2012

UK First Entry date: 10-Jun-2011 ( No Job )
UK Exit: 17-Jul-2011
( 100 days Break)
UK 2nd Entry: 25-Oct-2011 ( Started Working )
Tier 1 First extension: 8-Aug-2012 to 8-Aug-2014
Tier 1 Second extension: 8-Aug-2014 to 8-Aug-2016 (*if I get the approval *)
No breaks from 25-Oct-2011 till date.

1) What is the start date for me for 5 years continuous period calculation for ILR?
10-Jun-2011 -- first entry (OR) 25-Oct-2011 -- 2nd entry

2)If the start date is 25-Oct-2011,
I will have shortage of 78 days (08-Aug-16 to 25-Oct-16 ) to complete continuous 5 yrs.

Would I be eligible to Switch from Tier 1 (General) to Tier 2 with the same employer?

3) If I am eligible to switch from Tier 1 (General) to Tier 2,
Would I be eligible for ILR after completing the 78 days on Tier 2?

Could you please help
Many thanks in advance.