Hi JEgelaar. Since no one else has replied, I thought I'd give it a shot. Don't have as much experience as most of these guys on the forum, but I have learned a few things. I too come from road background (mostly smaller bikes) having loved road bikes in my teenage years. Now I have seen the light, life is so much more fun now
It's kinda hard to compare the 250 2 stroke to a 250 four stroke. I think coming from road, you will get into the swing of things quickly on the 250F. I think it will be good for you because I don't think it will tire you out too much, but it still has a good amount of power and will be able to do what you need it to. In other words a good all round bike for track and trail whilst being a beginner to off road. If you had to compare the 250f, you'd basically compare it to a 125 2 stroke and the 450f to a 250 2 stroke. But they are all different bikes. It is also up to preference.
Also ask people you ride with or other people what bikes they ride and how they use them. Learn as much as you can because you will start to understand the differences. I recently bought a 99 KX250 that I am busy rebuilding for technical riding. I chose a 2 stroke because it has a lot of power but still lighter than a 450 4 stroke making it easier to maneuver over very tech terrain, but the weight save comes at a cost of fuel efficiency.
I hope this helps a little. Maybe someone else can add to what I have said.
Ed