There's a number of things to consider here.
In short, I'm concerned about latency, parts compatibility, radio interference, and difficulty to set up.
Are you transmitting video for review later and flying the plane through line-of-sight, or are you trying to fly the plane from the video feed? I'm assuming you're looking to fly through the feed since the gopro handles recording already to its on-board storage.
If you were to get a video feed from your GoPro to your computer, how much lag would there be with this solution? RC with lag is frustrating at best and expensive at worst. Admittedly the GoPro could have some great video quality but from my understanding, the lag is very uncomfortable to fly with. I know that with the video lag from my Hero4 Session and Hero 5 Black, the video to my phone takes too long to get to my phone screen for my tastes. Sorry I don't have exact numbers here.
How are you planning to get the video feed to the application? It looks like
qGroundControl only supports UDP RTP and RSTP over a network socket read
here. You would need to change that 5.8Ghz analog video to one of these two protocols for qGroundControl to understand it and it doesn't sound easy.
The best documentation I could find related to this was here, and it doesn't bother using the 5.8Ghz transmitter you selected at all.
https://dev.px4.io/v1.9.0/en/qgc/video_streaming.html
Based on this documentation, it looks like they are using a single-board computer hosting a Gstreamer server and a 2.4Ghz wifi adapter to transmit the video. Most control links between your radio transmitter and the receiver in the plane are 2.4Ghz, which is the same band wifi transmits over, so your video uplink on WiFi could interfere with the signals from your transmitter controlling the plane from the ground. I hear that if you're using a 2.4Ghz frequency hopping protocol such as Spektrum's DSMX or DSM2, you'll probably be fine, but I'd rather avoid the interference in the first place. I wouldn't want a bad-control-link day. If you're not bothered by that and have the patience to set this up and get the gopro to work like the webcam in that tutorial, go for it and let us know how well it performs. I'm sure there are plenty of people with GoPros already that want to get into FPV flying cheaply.
You might even be able to use the onboard wifi on the gopro, connect your pc to the gopro, and play the live video using VLC player instead of qGroundControl, seen in this video tutorial
If you have the money to spare, you might want to choose a more typical FPV set up using an fpv camera and transmitter for your plane, and on the ground you would use a receiver, a display that won't "blue screen" when it detects a lot of static, and a way to power the two. You can buy cameras with transmitters built in, and there are goggles and display planels like the flysight black pearl that include a receiver, video recorder, video out, and battery pack all in one.
