Working Tax Credit

[Oisen]

Hi,
I currently live in the Rep of Ireland and i commute to work in Northern Ireland where i do 40 hrs a week

My details
Single
No Children
Over 25
No income in 2011 because i was student
Now working in Uk
Have National Insurance No.

I was told i may be entitled to working tax credits.
I rang the helpline and they sent out form which i completed and returned on the 20/8/2012, i rang HMRC twice and they said they recieved application and cause i was live in Ireland there is more checks than usual which have to be carried out and that was it, no eta on when it may be processed, it is now 23/10/2012 and still have not heard anything from them. i have a few questions i`m hoping that you may be able to help with

How long can it take to process a claim when working in Uk but living in another EU county.

What additional checks are carried out?

If i am enttiled to Working tax credit how much may i be eligible for?

Should i make a complaint on grounds taking a long time to process?

What documentation should i have ready incase they require?
(only forwarded application form, no other documentation was sent as it was not requested on form)

Who could i ring to find out more information on my complex WTC claim?

Thank you in advance for any help you can provide