I *really* find it hard to believe that you think that there is something wrong with specifying fees for services up front.
Nothing wrong, just uncomfortable when it involves shidduchim.
Is there a prevailing norm on either that is firmly established? I’m not so certain that there is.
There’s probably a range, and a beis din can probably only enforce the lower end of the range (as long as it’s not very atypical).
As far as time of payment, Baal Boose might be right, and if there’s no firmly established minhag, they parents can probably choose the later date, but I’m sure there’s no later date expected
than the marriage.