The display -
If you are a teacher and you want to keep doing this distance teaching for days on end, you'll soon want to see what your students are doing without squinting at a tiny screen. It's probably tiny because you need to have something portable to to show what you're doing with your hands and that means you can barely see what the students are doing.
This also applies to students, as the teacher is asking to get a good look at something, which often means you can barely see the teacher. That could be alright, but it might not be.
The answer, especially for teachers, is a second monitor, mostly because you can manage with anything for an hour a day, but 5 or 6 hours means eyestrain and backaches. A bigger one will let you see the students more easily, and if you teach group classes, they are indispensable.
You have choices - a big monitor, or a TV. Almost all new TV's can function as a computer monitor; if you are re-purposing an older one, you might need to check on its having an HDMI in port.
I bit the bullet and have a very large TV on my wall, that I can see from a distance, and shows me what students are doing. If you are using a windows device it is easy to set up a 2nd monitor. (In part 4 I'm talking about cables and hubs, which is how you connect the two) When I have a group class I can see 16 students at a time and it is beautiful! I don't know how easy that is from other platforms. I'd be happy to have an iOS person weigh in in the comments.
Depending on the setup in your studio, you may need a smaller monitor, and a means to mount it. Also in part 4 is a bit about stands - there are stands made that you move around, have wheels, and hold monitors. And of course there are wall mounts which let you angle and tilt your monitor for the best viewing angle.
Another work-around is logging in as second person in Zoom if you have a spare tablet, but this takes twice the bandwidth, and is prone to problems unless you have a really highspeed connection.
If you are a student with a laptop or a newer cellphone and a TV, you might consider connecting to your TV to see your lessons on, if your instrument can be in the same room. I'd do this if I had kids doing home schooling as well. It might also work for some teachers.
cameras - webcams - I've been through many versions, but now have the best set up I can imagine. I use Zoom with the share screen enabled. You can share anything - a video, a whiteboard to write on or a 2nd camera. I use it mostly in the 2nd camera mode.
That 2nd camera is perched on a stand and close to my harp so my hands are big and clearly seen by students. Zoom knows you want to focus on whatever you're sharing, so it makes that picture nice and big, and insets a little frame of the original camera used for talking and so people can see more of me. the 2nd camera is a logitech with a mic, The mic is not good for musical instruments, but you don't need to use that part of it. The camera is great and has its own autofocus system. Logitech C920 webcam.
The original camera easily, and most likely, can be your laptop/tablet/phone, and that will be adequate for many uses, but you can also use another stand-alone camera as your original. I used the first version of that for the past few months, using my surface laptop as the primary camera and the little logitech webcam as the share-your-screen one.
But things have changed for the ($$$ alert) better. I'm now using the Logitech meetup camera. It sits below the big screen on the wall and therefore is a lot further away from me than a laptop or tablet would be. This has a big advantage of letting me show things with my waving hands for rhythm or solfege or whatever. And it is much more relaxing to not have the camera right up my nostrils. I don't have to see myself in such a big way, and the stress is therefore lowered. If I need to stand to demonstrate something I can zoom out and all of me can be seen. It also has a speaker which I would use instead of headphones if there was more than one listener, and it also has a mic, which I'm not using. If you teach dance or movement it would be excellent. You control it with a very well designed remote control which lets you zoom in and out and has presets.
Using these cameras is a little finicky at first. I was confused by the fact that Zoom does its own choosing of cameras and mics, not Windows, but that is a big benefit, as you can custom make your best solution for Zoom that way. Once I found all the controls, life was good.