If you don’t have a Linux box handy for trying out / learning nfilter/iptables, maybe check out Digital Ocean for a cloud based VM. There’s also a decent intro to iptables on CentOs
Yes I recommend both Digital Ocean and https://www.turnkeylinux.org/ on the course. Good call.
Have you tried VULTR? Looks like they have FreeBSD. Don’t know about PFSense. Yeah, DO has FBSD too, but, you can’t upload/install your own ISOs so no PFSense (and they’ve been having performance issues with FBSD). I’ve tried Asterisk (PIAF/CentOS 6) on DO but ran into latency issues.
Not tried VULTR. I like Turnkey because of Debain and Amazon.