So we are actually adding imagery to our satellite so I think I can answer these pretty well.

For question 1, I do think you could use it for astrophotography. You could probably capture pictures of the stars if you have stabilization on the CubeSat. However, the photos would probably be similar to the photos taken of space from the ISS. What I mean by this is you might be able to take photos of the stars, but it wouldn't be able to see anywhere as far out as Hubble. I know a bunch of CubeSats use smartphone quality cameras so you would probably get a decent photo that might make a nice desktop wallpaper, but it wouldn't really compare to a bigger satellite. It would show an overview of the stars, but it wouldn't be significantly different from existing images imo except maybe it being from a different perspective. As far as zooming in, that would actually be kind of hard due to space constraints. CubeSats are small, like really small (10 cm x 10 cm x 10 cm in some cases). So it would be hard to fit any substantial zoom lens system in there. That might make getting ultra close ups hard. Maybe as camera tech improves in the future what you are suggesting would be possible though. Aiming it at a specific planet also might be a bit of a challenge. CubeSats mostly don't have propulsion (although we are adding an ion thruster in ours). They can use reaction wheels to rotate though. However, accurately rotating it towards a tiny planet in the sky could be hard. However, I will say you could go for a really big CubeSat design and fit a good camera system in that. Then if you solve the aiming issue you could get some really cool images that are zoomed in on planets / stars.

For question 2, we actually considered trying this. I had the idea to live stream the satellite on Twitch. We discovered that livestreaming it was hard. If you are sending data from the CubeSat to earth, the data transmission is very slow. That basically rules out livestreaming. Maybe you could transmit it to a big communications sat in orbit which then sends it to Earth. However, I suspect the data transmission speed might still be less than ideal. Plus, using a communications sat network (like Iridium) could be expensive. Let's say though communication tech gets better and you can transmit directly to Earth at a fast speed. There is still are two major issues. Regulations and getting ground stations. Every single ground station (basically an antenna on Earth that gets data from space) requires you list it on your FCC application. If it involves ground stations in other countries (especially countries the USA isn't friendly with) it can get very messy from a regulations perspective. Also, getting those partnerships to begin with can be messy as well. There are some networks like SatNogs that do allow for receiving data from volunteer ground stations in other countries. Although, I don't know if they would really be practical for livestreaming due to coverage. I know Amazon has some offerings where they let you access their ground station network that might allow for livestreaming one day. However, I haven't really explored too much into it. I also haven't heard of any teams using AWS Ground Station personally though. Honestly, you'd be forced into using Iridium regardless due to coverage being shoddy for ground stations. Overall though, I think the data speeds just aren't there yet to livestream, at least not with LoRa (which is the protocol a lot of teams use for transmission).