You can read this in a different unit, but I would say it's because when you have the article clearly stated (be it "de" or "het"), it's always with the -e ending (so, 'totale'). This happens here when you have "HET totale nummer" or "DE totale hoeveelheid". However, it's 'in totaal'. Hope it helped!
Not redundant in English, I am sorry to argue with you here. If you abbreviate the English sentence to "What is the total?" you are assuming the subject is the amount....but leaving it out means the subject is implied. Total is, in your sentence, the noun not the adjective. In the dutch sentence it is an adjective. If you leave out "the amount" the in the dutch sentence, I believe, you will find an "er" as the placeholder for "the" subject.