I think in my lifetime, I've set up at least 12 home theater systems at 5 different houses now, some for me, some for friends/ family. And I will say this, yes, in my opinion, getting surround sound is worth it. Even if you're streaming. Having said that, you have to make sure that your streaming device will decode the latest signals. So my streaming source is an Apple TV. I use that and am able to get Atmos through HBO, Apple TV, Disney, Netflix and Amazon. (Hulu stinks and I don't think they have anything over stereo to my knowledge.) I know the Apple TV works with the streaming and sound formats, I'm not sure if other streamers such as a Roku, or Amazon stick are as compatible with other streaming services in delivering Atmos sound. (You'll also need the highest Netflix tier to stream in Atmos /4k too.)
Next up is the TV. As others have said, if you want 85 inches, I think Sony is unbeatable. LG OLED and Samsung High end TV's compete with picture quality, but LG doesn't make an OLED that size, and Samsung doesn't support Dolby Vision. (And after switching from regular HDR to Dolby Vision, its game changing because your TV is automatically dialed in using DV and calibrated making the picture even better.)
As far as sound goes, every step up will improve your experience. I have yet to ever hear good TV speakers, like, ever. They just don't sound good. A soundbar is certainly an option, and that would certainly be better than TV speakers. And, most good, two channel systems with a sub are going to best most soundbars. But adding speakers to your rear, sides, and ceiling, that's where it really becomes an immersive experience. So a "basic" 5.1.2 system is, in my opinion, the best bang for your buck. But, I have constantly upgraded my system to where I now have a 9.2.4 system, and my movie experience is now far better than having fewer speakers. So, if your room would be able to support that many speakers, I'd suggest to at least wire up a 9.4.6 solution while you can and that way you have the option to put in more speakers if you ever wish to.
As far as speakers go, I have used Klipsch in-wall speakers, Focal's, but my favorite theater speakers are either Definitive Technology towers, or Golden Ear tower speakers. They both have built in subs, and their quality is great for music or movies, plus they manufacture complimentary speakers that you can use for surround and height speakers. Paradigm, Focal, Klipsch, there are really a lot of great options.
I disagree with a lot of people here though who say you have to get a pre/pro and separates to start. I think a high-end receiver that has built in amps is perfect for most scenarios. Or, at least to start. Just make certain it has pre-outs for all your channels so that, if you choose to, you can offload the signal to an external amp if you ever want. Anthem makes a great receiver depending on the number of channels you want to start out with that can decode 7.2 channels up to 15.2 channels. (But you'd need an external amplifier to power some of those channels.) Marantz, Denon, Yamaha, they all have some good solutions as well with built in amplification so your starting costs are a lot lower, and you can add external amplification if you ever choose to. (And if you eventually move to external amps for all your channels, then you can move to a pre-pro only which would deliver a great sound too.)
Anyway - that's my .02. One other thing of note too is your room size. If it's a small room, then 9.4.6 may be huge overkill. If the room is huge, that may not be enough. But yeah, with modern room correction software, good speakers, good sub or bass performance, in my opinion, I think it would be worth it to setup a multi channel surround system. (OH! And Music with Atmos, that's life changing! My two channel stereo sounds great, but when you get immersive audio involved, it's an entirely different experience.)
