Unfortunately, there is no way to do this via the system itself. You need to get a camcorder/phone/camera/etc. and record the screen along with your voice.
You cannot record gameplay with PlayTV, you can only record TV.
It depends what application you use to record PC gaming or console gaming (whatever version you play) For the computer I use Quicktime for Mac as it records gameplay and live commentary at the same time. For console I use a Hauppauge HD PVR to record XBOX footage in 1080p HD but no commentary. There are other forms of recording, which are freeware and shareware.
There is no video out on any 3DS model, the only way to capture video from one is to record the screen with a camera, or install an expensive hardware modification that splices a USB port into the wires that go to the screen.
Yeah
Look for the record button at the bottom.
There is multiple things needed to record and edit gameplay. To start off with you need some type of video capture card.Ranging from a bad quality easy cap to an expensive hd pvr. You also need a video editing software that you can edit and overlay commentary with after you record the game. You could also use a phone which is what sometimes starters use to record.
To check for unauthorized software in the 3DS system as well as to enhance gameplay. Sometimes, new features are added through these updates (Streetpass Relay)
You can't yet....
yes
With a DVD recorder I think.
Use a video camera.
The 3DS takes 3 1/2 hours to charge. The battery will then last around 3-5 hours of gameplay (depending on your settings) before you need to charge it again.