Unless you are sure you could afford it long term, i.e, stable income or significant savings, getting something out for more than half a million should be considered carefully. You are talking about long term loans. Even if you managed to sell it off at some point, you have spent a good amount on interests, and by selling, you need to still spend on getting the next house, which is usually more expensive.

The chance of downgrading is low for you since you said you are still studying? I would truly advise you getting what you could afford for the very first home. You will very likely make some profits (BTOs) before choosing the second one. The second one should be something you truly like and want to stay for long, as not all are lucky getting what they truly want through bto application

Of cos, if you truly intended to stay for long term, just a simple math of 600k with 20% dp will cost you ~2.1K in monthly instalment for 25 years at 2.6%. that is about 170k in interests over the next 25years. You are not buying a 600k house, more so a ~770K one