The official transportation website of the NSW shows only one option for traveling from the Sydney airport (International Terminal) to the CBD (intersection of Pitt St. and Goulburn St.), at least for the mornings of weekdays: train T8. However, Google Maps show two other options:
bus 420 to Botany Rd at Hollingshed St -> bus 310 from Mascot Post Office, Botany Rd to Central Station, Eddy Ave, Stand A
(I remember seeing this route, but Google Maps doesn't show it anymore) bus 400 to Mascot and then bus 310X.
The cost of T8 is around 18 AUD. How much would the above two options cost? Which of the two routes would be preferrable (faster/with more convinient transfer)? Are there other options not listed above?
Edit: also, can I just walk to the Mascot (or Wolli Creek) station? I mean, are there sidewalks and is the road relatively smooth so I can carry a full-size carry-on?