So, a big statement you through out, without likely understanding what it really meant in the real world was this:
" adding a sub. And other atmos/satalite speakers later "
Adding 'other speakers' later isn't a well thought out plan. It's like buying a car and saying I plan to upgrade the wheels AND ADD MORE WHEELS TO IT LATER!
Well, a car that's designed for four wheels, can't really have additional wheels added to it later.
A receiver is the same way. Some can handle Atmos, some can handle two or four Atmos speakers, some cannot. Reading about surround formats and the speakers utilized is important so you can understand the basics. But the most typical basic surround sound setup is five speakers, plus a subwoofer. Often called 5.1. The first number is the main speakers, the .1 is for the subwoofer. If you add Atmos speakers, then those speakers are added after the subwoofer. A full on surround sound w/Atmos setup and a couple of subwoofers may be referred to as 7.2.4 audio. But, you need a receiver capable of decoding all those channels of audio properly for your room, and those receivers are still stupidly expensive.
So, for now, one of the better values is that Denon AVR-X3500H - But, it is designed to power up to 7 speakers plus send audio to a powered subwoofer in some very specific configurations. Learn about those configurations before you dream up a room with 100 different speakers in every possible location. That's not how things work.
Quality over quantity is the goal. It is the talking point. It will be the go to on these forums and from almost everyone involved. There will be a ton of recommendations to do research before you buy. Always ASK FIRST - buy second. If you can't wait that long, then at least do some decent homework and read reviews if they exist before spending your cash.
I have found that good speakers are one of the best investments in audio that people can make. Not expensive speakers, but good speakers. Especially good subwoofers. A good subwoofer almost always costs a fair bit of cash as well. Throw out the budget when it comes to a good subwoofer, but a good subwoofer can be a thirty year purchase.