SET (LR); PLEASE HELP, VISA EXPIRES SOON

Hello Everyone, i am hoping i can apply for the SET(LR). However, im not sure about a few things of which i am hoping someone could help me out. I first came to the UK 01/04/2005 on a dependent tier 4 visa as my parents were studying and switched to an independent tier 4 visa on the 24/09/2013. My current tier 4 visa is due to expire on the 31/10/2017.

So, i would like to know:

1) Can i apply for SET(LR) if for a period of 6 months out of the 10 years i were on a visitor visa? - i am only asking this to see if i can apply for a visitors visa for a few months to help me and give me more time with my application.

2) When completing the form (Part D3, any absences from the UK). I have had 3 different passports and a number of different visas during my stay in the uk, however they were taken away from me by the authority when applied for a new passport/visa. The issue is that i dont remember the dates of which we left and returned to the uk each year and neither do my parents. So, what can i do here? I know for sure that i have not exceeded the 180 days at a time or the 540 days in total. What do you recommend i do?

3) Can i apply for the SET(LR) through the post even with my visa expiration date so close?

4)It states "You should also provide documents of the type listed below to show that you were continuously resident in the UK during any periods for which you are unable to provide a passport." However, the list provided doesnt apply in my case as i was still underage at the time and the only thing i can provide is a doctor's letter showing registeration but even then it would only show registeration every 4 years or so and thats when we've had to move to a new house and had to register at a new surgery. And so again im not sure what i should do?

5) Also i heard that i have to demonstrate i had comprehensive medical insurance for all of my time in the UK for my years to count towards the year requirement for settling, is this true? and how can i prove so?

I would very much appreciate any help i can get as my visa expires very soon.