All three options are doable in various ways, it's more of a choice of which one you prefer, what your skill level is and how much effort are you willing to put in.

Plex does not support IPTV directly but it can be made to work via a software emulation of a tv tuner (hdhomerun). xTeVe is free software that works very well for this.

There are lots of free legal streams that you can connect with. A great place to start is here https://thefrugalstreamer.blogspot.com/

Check the F2V link on the right side to find a great playlist.

I'm using a Synology NAS setup. I'm using the Channels DVR service (also installed on the NAS) There is a forum thread over there outlining how to get IPTV and Telly working with their app and I followed that (Telly in a docker). It may worked similarly with Xteve, not sure. I am able to get my OTA and IPTV channels working great together for viewing and recording. It's a paid service, but it works. Once I got Telly working and implemented, I then went through the process of getting it to work in Plex in hopes of eventually going the free route once I got the bugs worked out. The trick is that you have to choose a zip code in a major metropolitan area and select a cable provider that has most of the channels you have in your playlist such that you can match the EPG properly. Problem I am finding is I chose mostly FHD channels from my IPTV provider for my Telly playlist and it seems that Plex will either choke on them or play with no audio. Can't figure out the workaround so I plan to redo my playlist with non FHD channels and see what happens. Problem is that the Channels DVR solution works so well that I don't mind paying the $8/mo. No, I am not a shill for them, just enjoying more couch time with that solution. Still enjoy tweaking and hope to get the Plex option running smoothly soon though.