1. Because it's decentralized, the complexity doesn't increase by having additional nodes on the network. The complexity does increase to a small degree as seen by your node as you make contacts. I guess my answer to your question is it's very scalable.

2. I have a notification loop that runs once every three seconds. The result is the latency is about 1.5s from when I send a message to when it shows up on my contact's phone.

3. Because it's a self hosted network, the data loss protection is up to the person running the node. I added a cron script to backup my node node once a day, but someone might want something more frequent...or less.

Cheers.