Wah, the TP-Link TL-SG108 is about $35 on Amazon.
So the IP address will be the same as those on the router's port, correct?
Is it good (future proof) to get Switch that is POE?
The internal IP addresses on the LAN side will be assigned by the DHCP function of the router so devices will have different internal IP addresses.
As for the IPv4 address on the WAN side, yes you will only have one assigned by the ISP. The router has NAT function so that each LAN devices (including wireless clients) can communicate with host outside.
In the case of IPv6, if you go with M1 and Starhub, then each LAN devices (including wireless clients) should also have a public IPv6 address. For SingTel it is a bit complicated. ONT users should be able to set up 6rd to have IPv6 address for the devices. ONR users may have difficulties and may need to request from SingTel. MR/VQ/WC do not offer IPv6. Moreover by default MR users use CGNAT and same for new VQ users. So they do not even have a public IPv4 address unless paying for a static IPv4 address.