ATM networks in Singapore
 

You are over-thinking this.
Singapore is a global banking and financial centre ... there are ATMs sprinkled liberally around the place.
Having been there many times, I've never had an issue finding and/or using an ATM. And you won't either.
If you tried a Google search "Singapore ATM machines" or similar, you'd get myriad sources of information ... one of them.

STAR has zero associated ATM in Singapore, and most (all?) countries outside of USA.

Cirrus is everywhere in Singapore. Please refer to MasterCard ATM locator website.

Probably. I just didn't want to toss a $5 fee out the window on top of the transaction fee if I didn't have to.

No transaction fee for Singapore ATMs. Your bank of course may charge you a fee.
Any Cirrus/Plus/UnionPay card will work

Not sure how much time you have, but I would *highly* recommend a Schwab checking account if you frequently travel abroad. No foreign transaction fees at any ATM anywhere in the world. It is, in all honesty, the most valuable piece of travel gear I have. Can get local currency out of any ATM anywhere and be good to go without needing to exchange cash or pay any fees. No minimum balance helps as well, I just store a few hundred USD in there for emergency use stateside and then transfer over however much I might need before an international trip. Have used it dozens and dozens of times in Singapore, never once had an issue.

If you don't have enough time to open an account or it doesn't interest you, figure out which of your cards has the smallest foreign transaction fee and go with that. Maybe pick the lowest two cards to be safe. Finding an ATM in SIngapore is not difficult. In my experience, every major hotel has one and you can usually find ATMs in any mall or shopping area.

I have a TD Bank checking account that also does not charge fees for non-TD ATMs and they rebate fees charged by the ATM owner as well. I pretty much just have this account for travel

One advice/recommendation - some ATMs might display an offer to use currency conversion rate offered by that ATM or post charges directly using card's currency. DO NOT accept such offers - it is basically DCC and will end for you being charged 3-7% on top of the interbank exchange rate.

Three main local banks in Singapore are DBS, UOB and OCBC. You can find their ATMs pretty much anywhere. Any shopping center will have at least one ATM from each of these banks, usually stacked together.

Didn't quite undertsand ? So your suggesting use the local currency (SGD) option or choose your home currency ?

The ATM may - before dispensing cash - offer you the choice of being charged in the local currency (SGD) or your home currency ... the difference being the exchange rate used ... if local currency you should get a better rate (interbank) versus home currency when the local bank shows you much will be deducted from your checking/current account. The better rate option is always choose "local currency".

Does one really need cash in Singapore?

It all depends; for me, none of the places where I eat the uncle or auntie accept anything else.

Understood now..makes sense.

Let's hope that universal QR code will change this...

I can hardly wait to just scan and eat in SG as I do in CN now.

Just the idea of handling food and then money is not a good combination.