1. The service will send an email to person A saying "Someone wants to #wannaGoOut". As long as person B doesn't make a typo when copying the hash tag, this problem is solved.

2. Yeah, it's a nod to certain eras of web design, which I like, but other people won't care so I agree.

3. It's email-based in order to make it work for recipients who don't have the app.

5. In 2019, it's probably best to support Facebook, Snapchat, and Instagram as recipient addresses... somehow. Although most of those aren't technically possible. Those platforms aren't really great for building services on top of.