What should I invest in if I intend to invest using OCBC BCIP?

If you are still unsure, just buy the entire basket of stocks. The NIKKO AM STI ETF.

However, if you plan to DCA less than $500 a month, than consider looking at POSB Invest Saver instead as it is cheaper in terms of fees.

By todays standards commission fees of 0.30% (not to speak of 0.88%) seem already overpriced, even if regular small sum longterm investing indeed is attractive because of the DCA discipline

Compared to SP500 the STI ETF clearly underperformed, if at all then, would try the Lion-Phillip ETF instead.

Maybe You are better served performance wise by DIY ETF investing with a safe, cheap (0.00 USD commission fees) online broker like Schwab or Ameritrade (U.S. branches), when loosing the few monthly minutes for reeinvesting is O.K. for You. You should also look to convert-transfer any SGD/USD into USA by a cheap service like f.ex. Transferwise.

Small monthly transfer amounts would still be prohibitively (?) expensive in relative terms:

f.ex. 0.46 % on convert-transfering 500 SGD into USD with T.