There’s an article about ADS-B in this month’s Linux Magazine. It’s written for a European audience and mentions starter kits for those interested.
Since these signals are region specific, perplexity suggested these sites for Australian gear. @Belfry is our resident expert and CEO (Chief Education Officer) so I would value his views on whether this is a reasonable starter.
The Linux Magazine link was behind a paywall for me (well, it referenced a free article but then the link didn’t seem to work?).
They’re essentially all the same globally, with the exception of some smaller regional rollouts. There’s an excellent article up on SKYbrary that covers ADS-B worldwide in a lot of detail. I’ll highlight this from the description section:
The 1090 MHz Mode S Extended Squitter technology is used worldwide to ensure global interoperability. At local or regional level, other datalink technologies can be considered, e.g. the Universal Access Transceiver (UAT) system introduced in the USA.
I’ve got no experience with either of those web stores in your post, or with the specific RTL-SDR product, but I’m sure that those kits are more than capable of ADS-B reception and any other hobby SDR project you decide to pursue afterwards (e.g., AIS for marine tracking, decode your own images from weather satellites, decode FM/TV signals and set up multicast to distribute them across your LAN to PCs). FlightAware has a great set of instructions to get started and links to online stores too. This is how I first got into it in 2020.
You could also potentially recycle existing hardware if you have an old TV tuner around too. The kits include the RTL-SDR which has an RTL2832 inside it. You may already have one or more of them at home because everything is an RTL2382 
.