We are planning to go to HK with my husband this October 19-21,2013

We have an early flight on 19th and early flight back to PH on the 21st. We are quite unsure as to where to stay in HK since it is our first time (we are also in a tight budget but we'll make sure we have allowances, just in case...) Is it advisable to book an inn or hotel in advance? We would like to ask also of your expert advise on what places to go on our 2 day visit. Thanks in advance for the advice.