Dingoonity.org

what is the max internal SD card size ?

- Someone got a 400GB working, but smaller internal SD's are usually better because they have faster random access/read times. A good Samsung/Sandisk is your best bet for the internal. Besides, unless you're running Linux to mount the internal card's ext2/3 partition, copying many GB of files over FTP is very, very slow.

can you put roms on both the internal SD card AND the external SD card ?

- yes. But some emu's requires specific, fixed paths. Symlinks could work if that word doesn't sound frightening

I've heard that the HDMI doesn't work, but does the AV out to composite work?

- no AV, probably ever. HDMI is supposedly being worked on.

Can you plug in an external USB controller ?

- yes. Some work. TonyJih posted a video of this

Can you plug in an external USB stick to one of the USB-C ports and run roms from it ?

- seems like it should be possible but haven't seen any confirmed reports

<a href="https://web.archive.org/web/20210802142702/https://www.youtube.com/watch?v=CT_eSsLP8tc" target="_blank">https://www.youtube.com/watch?v=CT_eSsLP8tc</a>

HDMI has been shown to work. It was the scaling that wasn't implemented.

TonyJih (the main Anbernic/YLM dev) stated multiple times that Ingenic is working on the HDMI driver now, but if they don't make any progress soon that he'll take over.

<a href="https://web.archive.org/web/20210802142702/https://www.youtube.com/watch?v=CT_eSsLP8tc" target="_blank">https://www.youtube.com/watch?v=CT_eSsLP8tc</a>

HDMI has been shown to work. It was the scaling that wasn't implemented.

TonyJih (the main Anbernic/YLM dev) stated multiple times that Ingenic is working on the HDMI driver now, but if they don't make any progress soon that he'll take over.

You literally posted a link to a video from 2013. 
Obviously no one has been working on HDMI-out anything on this chipset since 2013, especially not Ingenic.
Ingenic will say *anything* to get people to buy more of their chips. 
It's common practice inside China to promise the world and then once you buy it to deliver nothing.

The HDMI chip is an external IT6610 from ITE Tech, I don't see any valid reason why Ingenic would write a driver for that, unless somebody pay them to.

Shouldn't the chip manufacturer themselves provide a basic driver for their own product? Else who would buy their chipset with no driver support at all?

The HDMI chip is an external IT6610 from ITE Tech, I don't see any valid reason why Ingenic would write a driver for that, unless somebody pay them to.

Who's to say YLM aren't paying Ingenic to do it? Clearly YLM are selling a ton of RG350's at the moment.

The issue is, the link is way back in 2013 and theoretically shows it works, why then for the past 6 years nothing has come out of it?

That simply means no one is working on it.

Uhh, what? I don't understand your logic.

The GCW Zero project crashed and everybody who continued the work did so as a volunteer - whereas the RG350 is a currently produced device.

TonyJih was paid by YLM to "adapt" the GCW Zero OS to work on the RG350. He says he's going to work on it if Ingenic doesn't.

He's actively contributing to the OS, buildroot and emulators:

https://github.com/tonyjih?tab=repositories

The RG350 is still a brand new product in its infancy - the first consumer units only shipped a couple of months ago. Of course there are no guarantees we'll ever see HDMI.