Yes, I did exactly this when I2P support was first in beta. I have a docker stack with Gluetun as my network for all my *arr containers and I was able to still point my qBittorrent to my i2pd router and it worked just fine.

Yes, absolutely. I have a VPS that runs a i2pd router and I can set my clients to point to my VPS and I am able to use the I2P network. In doing so, I had to make sure I forwarded the correct ports on my VPS so that it would reach the i2pd application. I will do a write up soon.