Anton - You guys are adventurous, same out here - cant wait for the snow to clear out already!!!
Since I have your permission I will post this up here to cover your questions on your project;
Here is the mock-up adding one LED Spot light. Since your main light is round it would look out of place to add a square light and there is not enough room anyway. I sent you details on this light.
Common practice is to add two Rigid Dually lights and attach to your fork clamps on the bottom using a simple flat piece of aluminium. The different prices are for (1) and the other is for (2) lights. If you go with (2) Rigid (SPOT RIG20221 or FLOOD RIG20211) it is $189.99. These are shock proof, waterproof etc. and have themal protection and limited lifetime warranty with Rigid. The kit comes with everything you need, wiring harness, inline fuse, heavy duty mounting brackets and waterproof