I had one for a while. They take a little getting used to, but it's not that bad. I eventually went back to a 75% for a couple reasons:

1. They aren't a true split keyboard, which means that the distance between the sides and the angles are all fixed. Maybe that just happens to coincide with the right position for you, but it wasn't enough for me, so it wasn't any more ergonomic than a normal keyboard.
2. They are very large for the number of keys they have.
3. Certain keyboard shortcuts, or just specific keybinds in games, are annoying to execute on account of the split.
4. It's harder, or at least usually more expensive, to find keycaps. You'll also need more stabs, which is more expensive and more annoying to lube.

So they're not bad and if you just like them, that's fine. But aside from preference, there's not really anything better about them.

I bought mine used, so don't take this as gospel or anything. First pair I got on eBay and they had horrendous imbalance and it wasn't even consistent. However, they have a pretty nice warranty and it is transferrable. Problem is the seller wasn't the original owner and didn't have the original receipt, so I just returned them instead. Bought a second used pair on FB Marketplace, this time from someone who could provide the receipt, and they have been just fine. Absolutely love them.

You'll need an adapter to plug in the mic as it just uses a single headset jack.

Yes, but it's probably not enough to power, say, planers.

The Steel series GameDAC 2 is (if you get the Xbox version) and it's decent. Not sure if they sell it separately, though.

This is an important point. Some headphones just don't handle EQ well, so you can't just EQ to fix things.

Muddiness usually comes from specific bass frequencies, typically the upper bass. So it's pretty easy to see on a graph which headphone is likely to be muddy. Same thing with treble, the specific spikes tell you which headphone is more likely to be unpleasant.

Yup, such is life with a big head. Although Sennheisers are pretty hit or miss for me because the cups don't swivel out at the top, so YMMV. Fortunately, most audiophile headphones that aren't Beyerdynamics get big enough for me.

The Q8 came with this. Honestly, I don't think it's that great. It's very stiff and is more like adhesive cardstock than tape, so the sound profile is a bit different.

I really like my IE300. I imagine the IE600 are even better, but I cannot justify spending that much on IEMs.