What should I do If I'm able to invest $2k-$4k monthly? I'm personally quite new to investing and $3-5k is already after deduction of all expenses? Quarterly Investment of $9k to max cash upfront fees?

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Google passive index investing.

Google Bogleheads.

Basically, if you think diversification is the way to go and you think you can't time the market, the bogleheads will probably fit right up your alley.

Essentially, they're all about finding a well diversified ETF that captures the whole world's stock market, buying that, and ignoring everything else.

I won't ask you to just follow blindly what they advocate, but have a read for yourself and see if you buy into their theory.

You should take your time, start up by reading some books on how to do investment analysis. Books i would recommend are one up on Wall Street by Peter lynch and the little book that beats the market. They teach you about how to do investment prospecting. After picking up the skill, then should you move to construct your own diversified stock portfolio

However should you feel you do not have much time to read up and hone the skill, i suggest you buy etfs to build a diversified portfolio. Etfs themselves are diversified as one counter holds multiple stakes on different companies. I would recommend sti etf first before venturing abroad to the s&p etfs and vanguard etfs

The quick way would be to invest into a portfolio created by a robo advisory based on your risk profile. Especially one that does rebalancing along the way.

If you have time, go read up on books like millionaire teacher or rich by retirement. These are written in our local context and are easy to digest for newcomers.