I'm using Plex client on 65A80J for a year now, so far so good. No crashes, Wi-Fi was rather consistent too handling the high bit rate files.
Currently holding off Shield 2019, was hoping for a Shield 2022 or 2023 but seems no news so far. Likely some new chip is upcoming perhaps.
I'm with the PS5 camp gaming wise

1) Yes, but make sure to set Sound Settings > Digital Output > Pass-Through when watching a BD movie on the PS5.
2) Yes, BUT there is a caveat. If your soundbar doesn't conform to the 40gbps bandwidth the Series X outputs, you will have to sacrifice for a lower bit depth and chroma setting.
3) If eARC is active, yes.
4) No it shouldn't.

I am unsure what soundbars have a proper HDMI 2.1a implementation, do your research. Unfortunately the mess that HDMI 2.1 created means that there are repeater devices (soundbar, AVR, pre-pros) that are equipped with anything from 24gbps, 32gbps, 40gbps and the full 48gbps bandwidth limitation. The PS5's HDMI 2.1 chipset is only 32gbps capable, where as the Series X is 40gbps. It's very important that you match everything in the chain so that everything is as compatible as they can be.

I won't tell you what to get because previously when I did for many other forumers, there are people who gets overly butthurt about it.

I will only tell you my opinion about your proposed setup and you can decide if you think that's the route you want to pursue.

Personally, I never liked soundbars and I continue to not like them because they are simply a compromise on the fundamentals of good audio. The HTA5000 sure on its own in relevance to TV speakers, it is a huge step up but it's like comparing a high school bully who thinks he's hot shit but when thrown into the real world is still just a kid.
Point is, if you have RM5.5k as your budget, why do you want to do Atmos or surround sound? You could get a pair of good bookshelves and settle for stereo until you have more funds to upgrade the system IMO.

The "up firing" drivers in the A5000 means you'll be relying on reflected sound for height audio. Unfortunately this barely works even in a perfect room designed for reflected sound reproduction. The way I see it, Atmos is not a usable feature on the A5000, you're basically buying a very expensive yet compromised 3 channel driver setup in a slim box.

But if the allure of having a system that is theoretically (not practically) capable of doing Atmos is too much of a sweet pot for you to ignore, then at the very least I hope you can place the soundbar and wireless speakers well enough. With the sub being wireless, you also have more freedom in properly placing the sub in your room to have the best bass response (and yes, sub placement is a very critical yet often ignored topic).

I googled these speakers... NEUMI CS5 USD70!?

But these brands I don't think is available here, unless you ship them in and that will cost some $ as well.

I personally have a 3.1.2 Q Acoustics for my bedroom, linked up yet.