Calculating tax basis with lender credit

1. When I purchased my primary home, I got "lender credit" from bank. While calculating the tax basis for my home, should I subtract this lender credit? or, ignore this number for tax basis?

2. What is the document, that IRS would require as proof of evidence for the "closing costs"? Is it bank "Closing disclosure"?

 

3. How do generally most people maintain the tax basis for home? I don't see any good tools for this. Any recommendations?