Oh jesus. Sorry googoogaga, the muppet brigade got to this question before we could give you some sensible advice. Let's start from the very beginning, the beginning is the best place to start...
I think you might be my favourite question-asker ever to appear in this forum. You've got a good goal (invest in the market for 25 years); you've got generally the right idea (invest in funds instead of single stocks); you've got realistic return goals (5% per year is totally doable); and you're not being suckered by the idea of actively trading your pot.
So, in answer to your question, what you want is totally, 100%, completely doable, and it's doable at very low cost.
The only thing I'd change from your original suggestion is that you should use ETFs instead of mutual funds:
Actually they do. Most mutual funds don't deliver enough extra performance to make back the extra 1.5% per year - so after fees, you end up underperforming a simple index fund. (And if you're targeting 5% per year, then 1.5% is a HUGE amount to pay in fees - that's 30% of your target return! No way, no how.)
If you buy ES3, the STI ETF, you end up owning all the stocks in the Straits Times index and you're only paying 0.3% for the privilege. (There are also ETFs that give you access to overseas stocks; we'll talk about those later if you're interested.)
My usual rule of thumb is "110 minus your age in stocks; and the rest in bonds". You can do that easily: 80% of your pot in ES3, and 20% in A35, which is an ETF that owns Singaporean government and government-agency bonds. The bond component gives you a nice bit of diversification; if stocks spew, like they're doing now, bonds tend to go up and reduce the volatility of your portfolio.
Wahkao gives bad advice. You'll see him popping up all over the forums dropping little nuggets like "there are 800 stocks on the SGX, you should investigate every single one of them and only buy low risk high return stocks" (of which more later).
This is, let's be honest, totally unrealistic for most people. You're absolutely right - you'll get a hell of a lot more out of just being good at your day job and earning promotions and raises.
And this "low risk high return" catchphrase... look, there's a story behind that. Wahkao goes around the forums spouting "buy low risk high return stocks" as the solution to everyone's problems without ever actually defining what it means, or how to find a "low risk high return" stock. Then this sophie.wee.weng character popped up, and we're really not sure whether she's a very clever bot or a very creepy stalker, because she's latched on to wahkao and started parroting his buzzwords.
If you see anyone on here saying "low risk high return", or "use FA+TA, both say buy then buy", or "don't be so hard up over {xyz}", it's not actual advice - it's the people on here riffing on Wahkao and Sophie's stupidity. You can disregard it.
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There's one other thing you can add to your investment strategy that will add a bit of juice to your returns, and that's a thing called rebalancing.
The idea is that once a year, you buy and sell your ETFs to bring them back to the "110 minus your age" ratio. Let's say stocks have a good year from here, and in 12 months' time stocks have gone from 80% of your portfolio to 85%. You'd sell some ES3 and buy some A35 to bring the ratio back to 80-20 (or, more strictly, to 110-minus-your-age).
(Why "110 minus your age"? Because as you grow older, you want your portfolio to be safer and less volatile, so you want to move it out of stocks (which give you more capital growth but more volatility) into bonds (which give you less growth but are less volatile as well). Also, the rule used to be "100 minus your age", but bonds are REALLY expensive right now so you don't want to be too heavily invested in them.)
The idea here is that indexes don't usually outperform for long stretches of time. If stocks outperform one year, bonds will generally do better the next year. If big stocks have a good year, small stocks will eventually catch up.
This doesn't work on a single-stock level - it only works on a broad index level. But if you're investing in broad index ETFs, a regular once-a-year rebalancing helps keep you disciplined, and it adds an extra 1-2% per year to your performance over the long term. That's a hell of a lot of money over 25 years!
So my advice boils down to:
1) Stick your pot into ES3 and A35, in an 80-20 ratio;
2) Once a year, rebalance to bring the ratio back to 110 minus your age;
3) Go to the pub.