if u will be near to damansara or subang most of the time, wait for LTE as they have LTE coverage over there. If not, just get the octa version.

Samsung Malaysia have only released the 3G i9500 version in Malaysia. Anybody selling the 4G i9505 in Malaysia would have imported it from the likes of Singapore etc., if you buy this sets, your warranty won't be covered by Samsung Malaysia.
Samsung has not officially announced when the LTE version will be released in Malaysia or what the price will be.

It depends on each person and their requirements. Depending on the plan you choose, you could either save money in the long run or be spending more money compared to outright + cheaper plan. It depends on what trade off you are willing to accept to save money. I have very little familiarity with malaysian postpaid contract plans so I can't really advice you on that. I have always been buying my phones outright. My malaysian number has been on the same old plan which provides very good value for more than 6 years haha.