Postdoc delayed decision! Possible reasons?
If the delay could possibly cause you to miss another opportunity elsewhere, then it would be a good idea to follow up. However, if that is not the case, then patience is suggested. It hasn't been very long and people often miss deadlines even when they don't mean to. It is a busy time of year for most academics. 

The question about the number of references is too local to comment on here. There may be a local rule, but certainly not a global one.