FPV beginner advice needed

I want to start flying FPV drones but don’t really know where to get started. I watched a lot of videos but can’t pin down following questions I have:

Should you start with an already assembled copter or should you build one yourself?

Which size is the way to go for <250g? 2“, 2,5“, 3“ and so on?

The drone would be for outdoor use. A drone for indoor flights isn‘t needed. Any feedback would be helpful, thanks :)