I wanted to start streaming with my new computer, to be built over the next few months. 
 
Is there really any benefit to going E-ATX, compared to just ATX when it comes to streaming? I know you get more features, and ect but I have a hard time justifying the extra costs. That is despite building a custom loop in a case that can support an E-ATX card.
 
The build I am going for is 3080ti, i9-11900k, 32GB Corsair Dominator Plat 4000.
 
What's your opinion, do you bother with E-ATX? Do you think I should if using it for gaming/streaming purposes?

CraptacularOne
EATX, ATX, iTX, mATX it really doesn't matter. That just denotes the form factor of the motherboard, not really it's inherent features or capabilities. I would be more concerned with correctly setting up your streaming equipment like capture card (if you plan on using one) networking gear and any pre amp or audio mixing gear. 
 
The base components of what you're planning look fine, the NVencoder on the 20 and 30 series cards is very good and you could also use quicksync and use the iGPU on your CPU if you wanted to go that route. 

I appreciate the response, and it has only shown me that I know even less than I thought I did.
 
I had planned on purchasing a capture card, but have not actually looked into brands. I don't know anything about networking gear, pre amp or audio mixing gear.
 
I don't plan on making a profit doing this. I have severe mental/physical disabilities and was hoping to use this as more of a social thing. I won't turn down the ability to make something from this, but already had plans to donate to random charities and giveaways.
 
 
This is what I had planned overall for my build:
 
Processor: i9-11900k
Motherboard: ASUS ROG Maximus Hero IIIV(Leaning towards, but not decided)
Memory: Corsair Dominator Platinum 32GB 4000
PSU: be quiet! Dark Power Pro 12 1500W (I wanted 1200, but can't find it anywhere, but I also think 1500 might be best based on power usage)
GPU: Evga 3080ti, preferably a version that I can connect to a custom water cooling setup
SDD: Samsung 980 Pro 2TB
HDD: WD Black 8TB
Case: 1000D
Fans: be quiet! Silent Wings 3 120mm x 11
Hydro X Series XR7 480mm Water Cooling Radiator x 2
Hydro X Series XR7 360mm x 1
EKWB Waterblocks and pump/reservoir
 
I then was considering a small form factor secondary PC for streaming. I was going to cannibalize my older computer for parts but would still need a new processor/motherboard
 
Processor: Leaning towards i7-11800k
Motherboard: TBD
Memory: 16GB Corsair Dominator Platinum (Recycled)
PSU: Corsair 1200w Platinum Rated (Recycled)
GPU: Was going to just use the iGPU
SDD/HDD: I need to look into which would be best, I do not want to recycle my old ones into this as they are already 5+ years in age.
Case: No preference, even considered just shoving everything into the 1000D, but worried about thermals
Fans: No preference
Cooler: AIO Corsair, no preference on model, depends on case, possibly even recycle my old one into this
Capture Card: TBD  

Rngmonster
I would not buy the 11900k, it's kinda a waste of money and PCIe Gen 4 is still marketing bs only. Not many people will make use of the Gen 4 speed for NVMe's and for GPU's there is still no benefit. Get the 10850k, 32gb 3600mhz RAM which is more than enough, you won't notice any difference going higher (unless you go for top benchmark scores), 1500w, even 1200w PSU is way too much and never needed if you are not going LN². 
If you want to watercool your GPU, just get the cheapest model you can get. Partner models are not worth the extra costs if you wanna watercool. 
A streaming PC is pointless and a waste of money these days. Just stream via GPU. 

this 

The i9-11900k I've heard can support higher CPU and RAM overclocks more smoothly with the right motherboard. Jayztwocents on Youtube may have a video on comparing good motherboards for that CPU. E-ATX motherboards feature-wise are certainly more lavish and could be complimented by the i9, but at a premium cost of course.

There are better cards for the price.

like others have said, just stream from the gpu.  just download obs or even use nvidias built in streaming.  it all works pretty good now.