ESA claim

I have fit notes going back more than a year, can I only backdate 3 months for NI credits?
The IRESA I am hoping to claim just whilst my buy to let flat is going through the sale process which started 3rd March. So I am not sure what backdating date I need?

Thank you, so I could actually make the phone call for ESA1 after April 3 rd if I backdated 3 months with supporting fit notes, and then if assessed eventually as WRAG I would still get the component that is being abolished with claims put in after April 3rd?

Yes it would be better to do it this week. I am wondering whether it would be simpler just to do the ESA claim for NI and then backdate it the 3 months. If I start trying for IR ESA due to capital disregard whilst my buy to let flat sale is going through,the claim would have to start from March, and it gets really complicated. I can manage if the sale goes through with no hiccups, if it goes through say in less than 4 months but if it takes a long time I may run out of money, I have already borrowed ten thousand. And it is things like the money I have borrowed that make the IRESA complicated, I mean really I am in the red but I do not know how the DWP will treat that. They will probably say I should have tried selling the flat sooner maybe? Once I get my 37 thou back from the flat say in 4 months time, it won't be long before it is gone because I am living off savings so if I just claim for NI now and forget the IRESA, if after assessment I am classed as WRAG, am I right in saying that when my savings have all gone,say in 18 months , I will get IRESA WRAG with the pre April 3rd 2017 component?

Also I have to pay out 2000 pounds next monday, rent/solicitors etc, so next week my savings would justify IRESA much more so than this week. Plus as each month goes by my savings are getting less and less. (until flat sold)So with IRESA, do you keep having to hand over new financial info as your savings decrease so that they can alter your award accordingly?