If I have $200 to RSP every month, which ETFs should I go for?

If you are looking to invest in VOO via RSP, you can consider using the FSMOne RSP. The transaction fee is fixed at USD$1.07, so it would be better if you can invest larger sums of money so that the transaction fee is not a significant percentage of your investment.

Since you have a long term horizon, you might want to consider growth ETFs outside of Singapore, as the STI ETF has limited growth potential compared to US ETFs. Putting more money into VOO would be a good choice if you can afford it!

If you're looking to invest in REITs and don't mind doing it with a roboadvisor, you could consider Syfe REITs portfolio. They have a 100% REITs portfolio and another portfolio that is REITs with bonds allocation. Since you mentioned that you're looking to invest over a long period of time, perhaps you can consider the 100% REITs portfolio.