Is it wise to invest into multiple platforms like different robo platforms or different regular saving plans?

Unless your total asset value is high, you will be incurring quite a bit of fixed overheads across multiple platforms

It depends. For example, you can invest in Autowealth for its 60% stocks - 40% bonds portfolio and Syfe for its S-REITS portfolio. This way, you have exposure in both the global market and singapore's market.

On the other hand, it might be a bit pointless to invest in 2 roboadvisors that invest mostly in the same products. You might as well leave the money in 1 roboadvisor and pay a single price.

I left out RSP because I think its fine to invest more in a particular ETF that you like even if your investment in a roboadvisor might have allocated some amount in it already. Just note that you're increasing your weightage in that particular ETF.