Urgent query on ltcg on sale \ purchase of residential flat

" I read that LTCG is calculated based on Selling Price - Current FMV of the Flat."

Its Sell Price --- Indexed cost of FMV as on 01.04.2001.  

"I have not approached anyone to do the Flat Valuation and provide me a Report for the same. Is there any physical Document or Report needed to be provided to IT Department for current FMV of Flat for calculating LTCG?"

No need to submit any documents just keep it for your records.

"In my case, how much will my LTCG come to?"

Based on assumption : FMV on 01.04.2001 as 8 lakhs......... would be around 26 lakhs.

" I registered my new Flat in Sept. 2017 and the cost is close to 1 Cr. After i received my Amount for my Old Flat in Jan 2018, i have put around 22 L Amount in my SBI Maxgain HL Account. Does this qualify under LTCG Saving?"

No, its not any such savings; and is not needed in your case.

"I will be using the balance amount to pay the balance own contribution to the Builder before 31st July 2018. So, don't think i will need to invest the LTCG Amout in Capital Gain Scheme".

Correct......

What all documents do i need to have or provide during IT Return Filing in order to claim LTCG Exemption?

No need to submit any documents while filling ITR

You need to have all sell & purchase documents with payment receipts in your records