honestly i'd just grab the Viltrox EF-EOS R Mount Adapter for $99... ring is probably a gimmick. and ProGrade Digital 128GB SDXC UHS-II V60 Gold cards are fine for r6 bitrates. gl!

Mirrorless bodies drain juice fast cuz of the EVF. Since you want that fast wildlife burst, your old gear might lag. In my experience: 1. Canon LP-E6NH Rechargeable Lithium-Ion Battery - Older ones wont hit 12fps. Unfortunately, my third-party batteries were not as good as expected.
2. Sony 128GB SF-M Series Tough UHS-II SDXC Memory Card (V60) - V60 is enough for 4K; V90 is highkey overkill.
3. Canon Mount Adapter EF-EOS R - Standard is plenty, i think? Ring is highkey distracting!

Yeah, picking up an R6 is awesome, congrats! I kinda went through a similar thing coming from an old 7D Mark II, that R6 is a whole different beast right? Like, for me, beyond the main power and storage stuff everyone's already talked about, I actually found myself really focusing on protecting it right out of the gate, especially if you're like me and mostly doing DIY maintenance. I mean, nobody wants to pay for sensor cleaning you know, so a good blower brush and some lens cleaning fluid that you just assemble yourself is way cheaper than those big kits, and you learn how to do it without stressing too much about scratching anything. And definitely a screen protector, like a basic tempered glass screen protector cuz those touchscreens are nice but they can get scratched so easily, and it's a super cheap fix and you can put it on yourself in five minutes. Also, I snagged an off-brand arca-swiss L-bracket for like twenty bucks on a flash sale, and it’s been a game changer for tripod work, totally worth looking into budget versions instead of the fancy ones, you just gotta check the reviews for build quality, sometimes they're surprisingly solid, sometimes they're kinda meh but for twenty bucks it’s not too bad if you’re careful.

Been using this for years, no complaints

TL;DR: Stick to OEM if you absolutely need that 12fps 'green icon' burst, V60 is basically the point of diminishing returns for this specific buffer, and maybe look into the drop-in filter adapter instead of the control ring. Honestly, the battery situation on the R6 is way more complex than it was back on your 80D. I mean, from what I've seen in the market lately, third-party brands like SmallRig or Watson are getting closer, but Canon’s handshake protocol is pretty aggressive. I think I heard that if the voltage doesn't hit a specific threshold, the camera just throttles your burst speed anyway? Not 100% sure if that's still the case with the latest firmware, but it’s something to keep an eye on if you're doing fast wildlife. Regarding the SD cards, I've looked at the technical throughput of the R6's bus—honestly, V90 is total overkill because the camera's internal write speed becomes the bottleneck way before the card does. V60 is basically the sweet spot for the price-to-performance ratio!!! And wait, before you settle on the standard or control ring adapter, have you looked into the drop-in filter version? I've seen some research suggesting it's a massive game-changer for EF glass users because you can just slot a CPL or ND filter right into the adapter. Pretty handy for a 70-200mm workflow so you don't have to mess with huge front-element filters.

Seconded!

Man I wish I found this thread sooner. Would have saved me so much hassle.