Tier 2(General) + Maternity Leaves +35 K +ILR

[nenygloria]

Hi,
I am currently on Tier2(General) visa and currently on maternity leaves for 52 weeks.
I got this visa in August 2013. so i am due for ILR in August 2018. I have many questions regarding ILR if someone can help me with it.
1)I have read continuous 180 days rule but couldn't understand it. first of all how many days can we be outside the UK in total 5 years and total how many days a single visit can we be outside the UK.
2)Since when i got this visa i didn't visited my back home . i want to visit back home on the following dates,
1 Dec 2014 - 20 Feb 2015
and then
1 Sep 2015 - 30 sep 2015
my question is would i break the continuous period for ILR if i visit that frequent within an year?
3) what is the 35K salary limit rule. Does i need to have 35K now when i have this Tier 2 visa or it would be fine if i just get this 35K just before the ILR? i mean in 2018?

your answer will be much appreciated.
regards,
neena