There is no way that any foreigners coming to HK will be able to learn Cantonese from scratch. Having a grasps of the basics is all that is needed. I say this in due respect that Cantonese is something that needs to be instilled from birth in order to get the proper tones. Unlike English, cantonese words cannot bw pronounced with different accents.
Take for example gau. Phonetically speaking coukd mean dog, but in another tone could mean 9 or even mean your dick.
After a certain age, people develop their own accents and parts of their throats become solid and hence our accents stays with us.i
To say learn cantonese like a local is near impossible.
Even some people who have been here a majority of their lives still have not mustered the tones.
I suggest just learn the basics to get by.