AppleTV requires that you already have a TV to connect it to.
If not, then a projector is a good idea. How portable it needs to be depends on your specific needs: is the room you’re playing in dark or bright? Is there an appropriate surface to project on or do you need a screen? How portable does the projector need to be? What’s the budget? Etc.
The groups I’ve been in which used projectors were mostly held in lass / meeting rooms which were all set up with commercial sized HDMI projectors. The exception was a classroom with roll down screens and an old-school overhead opaque projector. The teacher showed mostly paper files on it. I believe he also projected a laptop screen.
i have a several-year-old book-sized HDMI projector which works ok on a wall in a dim room for me, but which probably doesn’t have the oomph to project large enough for a lit room full of people. I’ve never tried it in a large room or with an actual screen. I’d expect the current crop to do much better, and they’re the sort of thing that will get discounted for seasonal shopping. There are some promising ones in the $200-$500 range. I’d look for 1080p and as bright as you can get for your budget. Assuming you’re only showing score sheets and not games or video you can make some concessions on colour and subtle image quality.
Also consider where you will put it and on what you’ll project it. If you don’t have a good, clear, light wall you may need a screen. If the room is crowded it may be hard to find a place for the projector that people don’t walk through. Most should have adjustments so they don’t need to be head on.
Software-wise is just use my normal music software. I use forScore and have a Bluetooth pedal so I can change pages without taking hands off my instrument. Just about anything will do though
