New to OLED TVs - LG B8S

[Eager Snake]

Hello there guys, how are you doing?
I've been pretty absent the last couple of... years I think, so, now that I'm finally getting up to date with my new man cave and all, I wanted to stop by and chat a bit about some things...

I finally bought an OLED TV, I wanted to buy a Sony, but it was really, really expensive, and the sale I got was for an LG B8S.
Actually, if I want to be completely honest, they had no stock, so I had to wait an entire week to get it. Today was the day and the screen was damaged, so, they had to order a new one and it's going to be arriving next week.
In the meantime, I have some questions that I hope some of you can answer.

First of all, I'm coming from an old Sony Bravia from 2013, I believe I can expect a HUGE change in terms of contrast and color.
The problem is, I don't have a 4K Bluray player, only my PS4 fat.
I bought a new HDMI cable for HDR, so I can take advantage of the streaming services like Netflix and Prime, but aside from that, I'll not be seeing any 4K Blurays anytime soon, at least for now.

I've read many many people commenting on 1080p Blurays on a 4K TV and they're all saying they look really amazing. Is that really true?

The other issue that I can think of is sound. My home theater is old now, I can only use optical for sound. Is there any way to set the sound up to have a 5.1 signal via the HDMI ARC?
I'm asking this because a friend of mine bought a new HT but he wasn't able to get a 5.1 from the TV, only a 2.0 and I'm not sure what's the problem, and he also has an LG TV.

I still have to receive mine, but I'm starting to freak out that I have to, eventually, change my entire setup.

So, yeah, that would be all, for now.
Video quality is my main concern, especially with 1080 Blurays. I'm dying to test Blade Runner, Blade Runner 2049, Alien and many many others in an OLED. I think it will look amazing anyway...

Hope you can answer me.
Thanks in advance.
Pablo.