Are the government benefits difference for 4 rooms and 5 rooms HDB flats significant enough such that it is better to opt for a 4 rooms HDB instead in the long run?

Are your earnings potentially more than the grants? Is your need for space and privacy negotiable? Everyone is different. only you can answer it yourself

Are your earnings potentially more than the grants? Is your need for space and privacy negotiable? Everyone is different. only you can answer it yourself

4rm receives more grant and assistance and demand for 4rm is also higher.

It depends on your needs and budget. For me, I would go for 4-room as it suits my needs. I will go for 5-room if I need more space. In terms of value appreciation, it depends on how many year lease the house Has, so just go for newer house with higher growth potential (check if there is any plan for near future in this area).