There are two ways you could do this - either in a live environment or via pre-recorded sessions. The latter gives you some scope to edit videos and add supporting material such as workbooks or tasks etc.

The problem with YouTube will be controlling who sees the content. I'd lean towards combining with an online course tool. 

I've recently created a free online course using Thinkific. It allows you to set up course chapters, upload pre-recorded videos as well as the supporting material, then communicate with students. Whilst you're building the course you can also put up a registration page where you can capture their email details.

Equipment can be as standard as a decent smartphone or digital camera, but you probably want to invest in something that will keep the equipment steady such as a tripod or phone stand and/or even a selfie stick. Lighting is a bit of experimentation, depends on what you've got for a studio.

Zoom is a good plaftorm for a virtual classroom in a live or pre-recorded environment. You can sign up for a free account, then start a session and record it for sound and video quality purposes. With art the harder part will be seeing the finer detail in video.

Hope that helps with a starting point for you :)    

    
  

Hi Lisa, after using the heavy Blue Yeti I found the portability of the Zoom H2n better to solve audio redundacy and clear audio. I try to have two sources of audio when recording when working solo. For recordings, I use Adobe Audition to clear up the background sounds. 
To get good line of eye I use a cheap iPad rig on a tripod or tripod clamp when not using a DSLR. FilMic Pro on the iPhone  with remote on the iPad was helpful for less fussy recordings. 
I prefer hosting on Vimeo becuase of the CODEC and admin control. 

I have been using Zoom to run an online writing group, and find it a very solid platform. I do recommend getting a paid account so you can go longer than 40 minutes (also dial-in isn't always working for free accounts due to the current high demand - there was a warning about this on their site recently).

If any of your art is digital art you may be able to capture your progress through the device. For example the Procreate app (for iOS) saves every stroke you make, then allows you to export it as a time-lapse video. There's one example of it here: https://www.youtube.com/watch?v=Xr2Dx80TU6Q

If you don't currently do digital art, it might be a good time to consider it as a diversification, as it will be easier for students to share already-digital work.

In terms of filming (physical) art, your challenge will be capturing and sharing at a high enough resolution that people can see the fine detail of what you are doing. That is going to be difficult for A3 due to the resolution and frame size you'll need. Alternatively, you could zoom in and film small areas of detail to show the method in those areas. Then perhaps display the full size work as a series of still images.

It might be worth using Vimeo rather than YouTube to host your videos as you can password protect individual videos - this isn't currently possible on YouTube.

I would consider a mix of pre-recorded lessons and live meetings because people are in need of human contact right now. If it's difficult to share visual material over the live meeting, distribute files beforehand (your examples/their homework) then use the live meeting time to discuss people's progress and challenges.