1. Never fly under Virga...quite possibly the most unstable air you would ever encounter. Think "microburst"! I can elaborate if you need me to.

2. Here are the official definitions:

V1 - critical engine failure recognition speed. V1 is the minimum speed in the takeoff, following a failure of the critical engine at VEF, at which the pilot can continue the takeoff with only the remaining engines. Any problems after V1 are treated as inflight emergencies. In the case of a balanced field takeoff, V1 is the maximum speed in the takeoff at which the pilot must take the first action (e.g., apply brakes, reduce thrust, deploy speed brakes) to stop the airplane within the accelerate-stop distance and the minimum speed at which the takeoff can be continued and achieve the required height above the takeoff surface within the takeoff distance. In this context, V1 is the takeoff decision speed.

V2 - takeoff safety speed. Also called takeoff screen speed, the minimum speed in the second segment of a climb following an engine failure.

3. Notam D is where you can expect to find the important stuff such as runway closures, nav aid outages, basically any ammendment to a published procedure.

4. Radar required for the approach. What do you mean, what does it mean?

Hope it helps.