Advice please: Should I buy HDB now and let it sit empty? Or buy later when I am ready to move in? What am I losing out for either option?

I'm not sure. But below are some things to think about:

HDB prices can still rise but the rise could be increasingly limited as HDB flats must remain affordable to most if not all citizens.

Serving a loan earlier than needed incurs opportunity costs.

I am not sure if wear & tear can still occur even if the unit is vacant... wear & tear = maintenance costs.

I am also not sure if you should be visiting your empty unit occasionally just in case, somehow, something happens.

The unit may be vacant but you may still want to opt for insurance...? I am not very sure about this part.

Newer flats are likely to have much more desirable features and amenities.

OPINON:

• Housing getting more ex. High chance more ex in the future
• BTO? U may not have the location u like.
• i would just buy and rent out the common room 1st. U can just make it "liveable", when you want to move in then do a proper renovation.