I went through this last year! I tried some cheap batteries but found my R6 only hit max burst speeds with the Canon LP-E6NH Rechargeable Lithium-Ion Battery. Im pretty cautious about power, so I stick to OEM now. * SanDisk 128GB Extreme PRO SDXC UHS-II Card: Fast, but pricey.
* Lexar Professional 1667x 128GB SDXC UHS-II Card: Cheaper, but slower clearing the buffer. Honestly, I'm just more satisfied with the reliability.

For your situation, first off, congrats on the R6!! honestly, that AF system is a total game changer for sports, ngl. i remember when i first switched from my old DSLR, it felt like i was literally cheating haha. i’ve got some thoughts on the technical side of the batteries and cards, but to give you the best advice on the budget vs. value stuff, i have a couple of questions first. basically, what’s your actual budget for these accessories right now?? and for the sports side of things, are you planning on shooting a lot of 4K video or are you strictly sticking to high-speed raw bursts? the reason i ask is because the technical specs for data write speeds change a ton—the UHS-II bus is basically required for those 20fps electronic bursts if you don't want the buffer to hang for ten seconds after a play. i've tried many setups over the years and it’s really easy to overspend on high-end cards you might not actually need... or worse, buy cheap ones that choke. tbh, a quick tip: for the batteries, the high-speed 'green' drive mode usually needs a high voltage draw that some third-party cells just can't maintain as they drain, so you lose your frame rate. anyway, let me know your budget and how much EF glass you're adapting so i can help you narrow it down! gl!

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just saw this thread and wanted to chime in on the adapter situation since i was in the same boat. when i first moved to mirrorless i was stressed about the cost of glass but honestly the basic Canon Mount Adapter EF-EOS R works flawlessly with all my old EF lenses. i didnt see the point in spending extra for the control ring version and saved a decent chunk of change there. for cards and protection:

• ProGrade Digital SDXC UHS-II Video Speed Class 60 (V60) is a solid middle ground. i use them for track meets and they havent failed me yet.
• ULBTER Screen Protector for Canon R6 is super cheap and does the job. i actually scratched one on a fence last month and it totally saved my actual screen. if you want to save more check out sites like MPB or KEH for used adapters. you can usually find them in mint condition for way less than retail. basically just stick to the basics first and see what you actually miss from your old setup before overspending... it saves a lot of headache in the long run.

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