Should I save with DBS multiplier or where else should I put my money? The condition of maintaining $3000 per month, is that the net balance or total sum of transactions (in/out)?

3K is the daily average balance just like any other bank account.

Besides DBS , can also consider other bank accounts of high interest. Use Seedly calculate to help determine the best account for you :

https://seedly.sg/tools/savings-account-calculator

If you just started working, I don't think you will have to maintain $3k per month as it is waived till you're 29 years old. Refer to: https://www.dbs.com.sg/personal/landing/dbs-mul...