I really like this OTG one because it's small and just plugs in the back without being a cable, just make sure you pick the one going to the correct direction, else you can't plug in a memory stick anymore because the hdmi cable would be in the way:

https://www.amazon.com/AuviPal-Powered-Adapter-Charging-Streaming/dp/B07TX8FY6W/ref=sr_1_28?dchild=1&keywords=USB+OTG+Cable&qid=1607592884&sr=8-28

If you really want an OTG cable get this:

https://www.amazon.com/Adapter-Streaming-Logitech-Keyboards-Nintendo/dp/B07ZF6KSTR/ref=sr_1_21?dchild=1&keywords=USB+OTG+Cable&qid=1607592884&sr=8-21

Then just get a good usb-stick, NOT and SD card:

https://www.amazon.com/SanDisk-256GB-Ultra-Flash-Drive/dp/B077VXV323/ref=sr_1_11?dchild=1&keywords=sandisk%2Bmemory%2Bstick&qid=1607593384&sr=8-11&th=1

^I like this one because it's small and in combination with the OTG I mentioned first wont stick out further on the side of the console.

Size?

Depends on what you want to put on there. If you stick to 8/16-Bit games 32 or 64 GB should be more than enough.

^This should be more than enough for the stuff you are planning to put on there.

If you are planning on also putting PSX games or so on there go for at least 128 GB.

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But hey this is just my opinion, you are free to mix and match.

Also you should have zero C8 errors if you don't put too many games in one (sub)folder.

Try these:

https://www.amazon.com/AuviPal-Micro-USB-Cable-Power/dp/B07FY9Z9GD

or this

https://www.amazon.com/AuviPal-Powered-Adapter-Charging-Streaming/dp/B07TX8FY6W

plus this

https://www.amazon.com/UGREEN-Ethernet-1000Mbps-Nintendo-Chromebook/dp/B00LLUEJFU/ref=sr_1_9

and this

https://www.amazon.com/SanDisk-32GB-Ultra-Flash-Drive/dp/B077VXV323/ref=sr_1_5

and you're good to go. I have this setup on 9 different systems, all work flawlessly. Move all your apps to the disk (disk set up as extended internal storage) thus freeing up space and improving performance. The internet adapter you show has a limit as to the allowed speed (100).