Rent Issues

Usually renmt is paid for the time you use the place, but since contracts are freely negotiable other arrengements are possible by mutual consent.
Rental contracts do not have to be in writing, but verbal contracts are of course more difficult to handle in case of a dispute.
If the relationship already looks difficult before it really started, I recommend you look for another place with a better landlord instead!

It's quite common here, on which date both the tenant and the owner agreed to occupy (agreement date not necessarily is your moving date). e.g. Owner X and Tentant Y agreed the date should be February 1, 2018. However, due to some reason tentant only can occupy on February 5, 2018. But, as per the agreement it will count from February 1, 2018.

Sub letting unit in most of cases are not regulated as it's not mandatory to sign an agreement, no stamp duty payment to the government, Nor PUB bill come under the tenant's name.

As Beppi said, if there is a dispute with the owner at the beginning then better look out other places. Plenty of sub-letting units are available for single person like you. Good luck