Hey there, I can probably help. I have built a couple of bird models and have studied bird anatomy quite a lot. When I get the chance I can give you a paint over, but for now a few tips-
The back of the head is too large, the back of the skull should be farther forward
The shape of the eye is pretty good, but he needs a supra-orbital ridge, or eyebrow ridge, right above and in front of the eye
Do you intend to keep the mouth closed? I can see you have modeled the mouth all in one piece. If so, the line between upper and lower jaw should be more defined, and there should be a raised area, or lips, around the part of the mouth that extends onto the head behind the beak
There should be more of a bend at the ankle so the leg doesn’t look so straight. By the way, the ankle is the part that a lot of people think is a “backwards knee” in birds. The real knee is actually higher up, hidden up near the chest of the bird.
From the above view, the flight feathers should be swept back a bit more, closer to being in line with the body. Basically, the tertials and secondaries closest to the body should be parallel to the body and they slowly fan out from there to where the outer primaries are about 45 degrees from the angle of the body
As for your question about alphas, I would say definitely use them. I have had good luck with it. As far as double sided, I had better luck with single sided as long as the pattern on the feathers is the same above and below. It is a tiny bit tricky to get both sides to line up.
Body feathers can be tough. I don’t have too good a solution. You might want to check out “dodo master”, a free plugin I used with some good results. It just has a tendency to slow things down a whole lot in the viewport and in rendering. Also can only be used on nurbs surfaces, so you must model nurbs under your model to attach the feathers to and then constrain them to the polygonal model with bind constraints if you are planning to pose or animate the model.
Anway, good start. I look forward to seeing how this progresses.