Currently in my first year of work and have been investing 25% of my monthly take-home into POSB invest-saver & bonds (80% into STI ETF , 20% into SSB) and 25% into savings. Looking to diversify out of SG market once it hits $10k. Suggestions?

U don't need to invest in overseas. even local can have good investment tool. looking at etf and ssb it only earns u max 5%. if u have cash u can put at other platform like seedin. they are offering 10% P.A. this is the highest i see at the current market compare to stocks saving bonds etc.

You may consider SPDR S&P 500 ETF which listed in SGX...

You could try out robo-advisors for US exposure. Alternatively you can also get HK stocks.

Yes, you should diversify into overseas markets such as China and US equities and bonds.