Need advice on Jellyfin setup

I'm kind of a noob at this so I just want to make sure I'm on the right track. Most of my experience is centered around using public trackers and qbitorrent with a VPN on my laptop and Android phone (using flud).

I would like to get started using Jellyfin to serve up media in my house and occasionally remotely with my phone. I have an older HP desktop that was formerly a business PC. I am currently resetting it back to a fresh install (probably Windows 10). I was thinking of putting Jellyfin on there and setting up Tailscale. I have already tested setting this up on a different computer just to learn the setup process and I got it working and was able to remote connect with my phone. I have Cox cable internet and I'm using their provided modem/wifi gateway so I probably don't have many options for customizing that other than port-forwarding. I also don't really need to set up any automation to download media automatically at this time. I basically want to be able to download movies the way I currently do and put them on the Jellyfin machine. What else do I need to know/do? What am I missing? and will I be able to just pull up Jellfin on my phone and cast media to my smart TV's (they do not have Roku btw)?