Help me regarding transportation from Novotel citygate, man tung road to Causeway Bay?

I am an Indian passport holder.
I will be staying for 3 days and 4 nights at :HK Hostel A1, 3/F, Paterson Bldg. 47 Paterson St., Causeway Bay.
I have to attend a conference at Novotel City gate, Man Tung road... DAILY!!!...I understand it will be an expensive one..Can anyone please suggest me how I can use Octopus card or whatever cheaper to save money from draining out of pocket??
Can I buy MTR travel cards at the airport itself?
Any idea how much HK$ should I carry to help me survive with fooding and 1 day sightseeing within Kowloon and Causeway bay area ?
Any help and suggestion will be appreciated.
thank you