Hey, I've debranded/flashed my W810i before, but this is a different phone so I'm pretty sure the steps are different.
I've already downloaded the A2Uploader, now I'm just having trouble finding the right firmware and other customization packs that I could maybe use.

Could someone tell me which firmware I should use?

The flashing procedure is the same on C905 as on W810: flash Main+FS+Custpack.

You can also use SEUS to unbrand the phone, by using a generic CDA