I have a similar setup for many of my bird pictures. There is a privet bush about 20 ft from my bedroom window, and I've placed a couple of feeders in/by it.
Caution when using flash - some birds are far more tolerant of it than others. Birds are suspicious of any disturbance in their neighborhood - a blind, a vehicle, an open window, flash, etc. (I use them all), and it takes them awhile to become accustomed to any changes and start returning to feeders/bush/nesting site after they have been disturbed. You will be able to capture some birds with flash, but many others will be frightened by it and stay away from your "studio." I use flash very judiciously when photographing birds.
Naturally - patience is a must. When I'm photographing birds, I make sure I have a comfortable place to sit if possible - a lawn chair or stool in a blind (along with water and snacks, a good fat log, a comfortable seating arrangement in the back of an SUV, or a comfortable chair by a house window.
Other less expensive gimbal solutions that are also less elegant than the Wimberley models, but still superior to a ball head, IMO, include the Manfrotto 393 and an Acratech Long Lens head.