First: Welcome! Sit back and be prepared to learn and spend!
As for the dark spot, it is a result of the bulb. If you 'frost' the bulb it will take out a lot of the artifact. A lot of people around here use something called Armor Etch (made for glass etching) available at many craft stores.
I personally just use sandpaper and sand up about 2/3 of the bulb. This is high enough that the filament should be covered by the frosting and shoot light straight out the front of the bulb.