Translation "We have no soup for him" was not accepted. This seems equivalent to "We do not have soup for him" (above), or "We have not got soup for him" (translation given by the program). If there is a difference, I am curious what it is.
That is a wrong question. Most Czech words can either be stressed or not. Obligatory clitics can only be unstressed and some pronouns either behacve like clitics or can appear in the strong position. See the Tips and notes for the obligatory clitics.