I’ve just started working and with that I also started learning how to invest. Currently, my plan is to RSP $100 into STI ETF, Stashaway and Syfe per month. Would that be a good starting point?

I wouldnt recomment Saxo for foreign ETFs due to the higher fees. Instead look into using SCB or IB, the fees are lower. IB is better if you're planning to do monthly DCA, if not SCB for more infrequent DCA (i.e. quarterly/yearly etc.)

Seem good