CFW doesn't mean it starts at boot, it means that the firmware was altered in some way, shape or form to change the user experience (hence "custom"). Granted, most current CFWs don't really add much aside from patching sigs but that's beside the point.
Nothing is changed. They are just apps that do OTF patches. Calling these apps custom firmware is like calling Priiloader custom firmware.
How many consoles do you know of that have had new operating systems written for them? Every custom firmware will be based on an official firmware. With more or less changed.
Just because a lot of people do it doesn't make it accurate.
Technically all the Wii did too was patch what was in memory. They just happened to do it very early and near seamlessly. And even the Wii didn't patch much, basically just sigs and that was it. Don't forget though that emuNAND and whatever arm9 weirdness rxTools has going on is probably more than enough to classify things as CFW.
1) The Wii did have custom firmware. It was called a cIOS. It also had custom interfaces like postLoader, although those weren't actually firmware.
Not that I know of. If you have ninjhax and 9.2 or below, you can downgrade the whitelist to allow playing blocked NDS flash carts though.
Yes, but don't sell it unless you really need the money. It might come in handy later, you never know what the gateway team might come up with.
To stack on what JoostinOnline said, if you use ThemeHax autoboot with a DS flashcart (or just Gateway Blue card since that's all it is) then upon exiting the game the system should automatically go back into EmuNAND (as exiting a DS game is a console reboot), which is about as seamless as you can get.
