1 full week will be ideal for a relaxed hk trip 

go with the 1st flight & back afternoon. since already pay for the flight you only need folks out more on hotel for staying more days. There are RM300+/- decent hotels near MTR 

I have been in HK 6-7 times. with 1week you can go many places without rushing e.g. can even spend 1-2 days @Macau.

It looks like 7 days but effectively < 6 full day because 1st day after check in about 2-3pm & the last day you gotta leave for airport on the morning/ noon.

Oct-Feb is best for HK because cooling & less rain 

in terms of weather, oct to feb is the best time but among this period my fav in to go before X'mas & back on or after NY due to the festival feel & decoration. BUT will be very crowded everywhere you go, even go eat also hard to find table sit 

If limited budget maybe can't afford Disney/ Ocean park ticket. If you don't go these places it will be pretty affordable to just eat & take MTR. I walked a lot too since not rushing, I didn't pay for any transport inside Macau because there is free buses @ferry to hotel, then I just walk the whole Macau with wife. Anyhow have to pay for ferry from HK to Macau both way la 

Economy class ferry ticket is hkd140 per way. Haven't include the time and Expenses to take travel to ferry terminal. Each journey 45mins to 1hr.

If u get hkd280 which is roughly rm140 cheaper then why not? But do consider the time spent.

Had you booked your flight? If still considering, I guess is better to go in 1 place, get out another place. Instead of waste 2x ferry hours.
By the way, if not mistaken.. macau and HK flight difference not much if compare to the time wasted.

This March, I will be going in through HK and getting out from Macau. 2N in HK and stay 1N in Macau. So now gotta making full use each minute of my travel.

You may try click one way ticket to Macau then another one way ticket back from HK, or vice versa. Then you save 1 trip of ferry