Im not good with json, or vb4 for that matter, but I literally JUST finished making a product that one of the features is grabbing the count of post a user has made in a thread. So if its of any help, or gets you in the right direction take a look at this product for vb4 that is able to pull post count of a user in a thread (its what i just used as my vb3 base). hopefully it will help.
https://vborg.vbsupport.ru/showthread.php?t=285293