1. Are there any other projects I should be aware of?
There is also Esplora which is based on Electrs
2. Can I use Electrs to serve random users from across the internet like I can with Electrumx?
3. Can I create a Tor hidden service for both? Clearnet is not an option.
Yes and yes as far as I know.
4. What are the general benefits and drawbacks for both?
There are performance issues with Electrs
https://blog.keys.casa/electrum-server-performance-report/So depending on use it might not be able to keep up with requests.
For you and just a few users it may or may not matter depending on how much you will be using it.
-Dave