First, binoviewer will no do much for astigmatism and the best way to manage that is either find long eye relief eyepieces or use Dioptrix.
Next, I am going to say a lot of things the might discourage you, but I am going to suggest that you still try it out for planetary observing because this is where BVs really improve visual acuity.
With binoviewers in the C8, even with the most optimized light path length (96mm for a William Optics or similar BV, a T2 adapter (2mm), a T2 diagonal (38mm), and a 15mm SCT to T2 connector, the light path will be 149mm, and this will make the focal lenght of the EdgeHD 8" about 45mm longer than the nominal 2125mm so figure 2175mm, and this is using a short light path binoviewer.
The concern I have about the EdgeHD is that in mine, the aperture was decreased if the back focus was allowed to go over 170mm. This means that if you use a standard 1.25" visual back (about 25mm of light path) an standard 1.25" prism about 65mm of light path) and a 96mm light path binoviewer (WO and similar) you are over 170mm, so you might get some aperture reduction. (also, the 185m of light path raises the focal lenght by another 80mm or so (maybe a bit more).
Now, I measured mine, but someone else said that they measured theirs and did not see reduction until over 200mm of back focus, so maybe it is a sample to sample variation thing. The only way to know for sure would be to measure it.
No reducer configuration will give full aperture and that means that the secondary obstruction goes up as a percentage of the (remaining) aperture. Also, the spherical aberration may increase slightly.
Now as I said, I still think you should try it out, and here is my advice.
Buy an inexpensive used William Optic or similar binoviewer and get a pair of eyepieces that best match your typical seeing conditions. For example, if you normally use a 12mm eyepeice to good advantage, then get a pair of 25mm Plossls.
Use the 1.9x or 2x Barlow on the binoviewers and use a 1.25" standard prism diagonal. This will fix any concern about aperture loss or SA.
Try it on Jupiter. If you like it, then worry about the path forward. If you don't you can sell the BVs pretty much for what you paid for them. If you do like it, you can still sell the BVs for what you paid for them and upgrade to a better BV and a good T2 (T2 prism, and better BV.
I would say that trying it out should be your first step and if you like it, you can decide where you want to go.
For planets, even an inexpensive BV and the included 2x Barlow, when used in your 1.25" standard diagonal, and a couple of inexpensive Plossls might be all you need (I recommend zooms as next purchase for planetary work).
Now you can use this without the Barlow but again, you might (or might not) loose a little aperture, but you still get a wider field, and that will be worth 3-4mm of aperture loss. Use the Barlow for planets though.