In the US, we are “limited” to 1000 mw in the bands that DJI operate. For analog, it depends on the channel and whether you have an amateur radio license (HAM).
As for range with FS, I have HDOs which means they are only goggles, the range question would be for the module. I have tried several and settled on ImmersionRC. Since you brought up range, what control link are you planning on - unless it is something like Crossfire or Ghost, your control link is going to be something you want to outstrip your video. With DJI, the control link and video share the same data stream, but you get feed back when you are reaching the limit, normally well before you lose control link.