For options (SPY/UVXY) I cut losses at -30% and start to trim some profits at +55%,

for stocks I cut losses at -12-15%. Profit trim at roughly the same. (+15-20%)

There are agencies like SIFMA and others who comb through the MBS data and publish it to paying firms but he also was the head of a hedge fund with access to all MBS Bond market disclosures reporting data which included whether the loan was fixed or subprime adjustable and also whether there was a positive Loan to Value # (Number of days late).

The scene in the movie is actually really well depicted on how this unfolded cause from there he literally spent days going through thousands of individual MBS / CDO disclosure bonds hunting for those two correlating variables and afterwards came away convinced that the bonds were absolute shit because so many of the packaged contracts within were leveraged against subprime loans that were already starting to fail en masse and would soon start defaulting.