Let's start with the posts. Using whatever aids you have at your disposal (I use the GRS Solder station with dual 3rd hands), solder the 20 gauge wire into the posts using hard solder. Careful to be sure you don't melt the post or wire, and be sure to draw the solder into the depression made with the drilling in step 2. I learned this trick (making an improved joint by creating the "seat" for the wire) from Lindsay Minihan of Metalwerx.
Now the connection needs to be finessed. This can be done via filing with a needle file, or you can forge this a bit into a graduated taper, then refine with a file. I like the later approach as it hardens the connection and if there is a challenge with the solder joint, you'll find it when you forge, and you can correct it at this stage, it will be more difficult to fix as you move forward with construction.