If I am looking to invest in ETFs each month, is the best way to invest through a bank (POSB Invest-Saver/ OCBC/ etc)? Or are there better ways you would recommend?

What about current times?

With TD Ameritrade or Charles Schwab, just examples, you had 0.00 USD trading fees, so could sacrifice 5 min for that monthly (15-30% withholding tax on dividends though) and do it cheaper all by yourself

Currently, FSMOne is offering an RSP program with one of the most competitive rates (0.08%, 1 SGD minimum), so you might want to consider if you are ware of the costs. Typically I try to keep my commission fees lower than 0.2%.

You can look at philips' sharebuilder plan. It allows you to invest in different counters and the best part is you can reinvest your dividends back into the same counter to allow for compounding to take place.