please help: going to Shanghai via Hong Kong on 06 Oct and back to spend day in HK on 14 Oct

can I buy the On-loan Octopus Card at Airport on 06 Oct to use on 14 Oct? (to save time on 14 Oct)
[deposit 50 plus value 100]?
I want to take bus S1 from Apt to Tung Chung [3HK$]
then up to Big Budha with Ngong Ping cable car (return) [135HK$]
then MTR to HK [??HK$]
ferry across harbour back to Kowloon [3HK$]
and get bus in Salisbury or Nathan road after light show, back to Airport [33HK$]
will 200HK$ value on the card be enough to cover MTR from Tung Chung to HK?
does my plan sound good?
any other suggestions?