[Holub]

Hm, I don't use BCSE multiple add mod and I don't know how this `add to cart` function is realized in. But I can tell you simple logic: when you click add2cart you go to cart.php?mode=add and after product is added you redirecting to cart.php via func_header_location function. You should change cart.php and check, if referrer contains 'cat' variable and this variable is less then 5 then you should redirect customer to home.php?cat=$cat+1 (of course, $cat - extracted variable from referrer). Else (cat is equal 5) you should redirect customer to cart.php?mode=checkout.

I'm not write code sample because you have installed module I'm have not.