I have around $500 to invest monthly. Looking to do an FSMOne RSP into VOO or VT, or should I just go with a robo-advisor? Thinking about the costs incurred by both and if it is a long-term option.?

Excellent choice to invest periodically 500 $. Yes, possibly VT or SWRD is all you need. The higher the dividend yield of your ETF the more relevant differences in U.S. (30%) versus Ireland (15%) withholding tax. But then you should also calculate in differences in trading fees and other fees of your broker (custody, account maintenance ...) for non-U.S. ETFs. TD Ameritrade (also Singapore branch) currently has no (0.00 USD) trading or other relevant fees, for U.S. stocks/ETFs, other brokers will follow.