(a) Yes, but the unmarked form is 'how big'. If you say 'how small', you must already have an idea that it is smaller than standard.
(b) Yes, both OK, but again, the unmarked (objective / noncommital) form is 'how late'.
(c) I don't read Portuguese (is that Portuguese?-- I know, we've had this conversation before, but I have forgotten already, Emanuelli. What is the definition of a unilingual?-- an American!); however, the only reasonable choice is 'how long is your hair?'
(d) I don't understand, so it must be wrong. 'We're out of gas'?