CC think you are an overly anxious expectant mum bless you
Cats dont have waters that break like humans,occasionally a cat will pass a small fluid filled sac before the first kitten is born but not always.
First signs of labour is often a missed meal, there may be extra trips to the litter tray and when labour is under way you see the contractions in the form of ripples along her body.
Honestly the only thing you may smell is your own body sweat through stress
Usually there is very little mess,and most cats produce without problem,it is a good idea to have vets details to hand incase of emergency and maybe read up a little.
Not sure of statistics but I would say about 1 in every hundred pregnant ones i`ve dealt with have problems. So Good Luck and try not to worry