before making animation, one has to visualize everything in its mind. once the idea is clear, animation is not a problem provided you have necessary know how about animation tool you are using. If the idea is not clear, it will takes you ages to make an interesting animation.
everything is possible. there are millions of freelance webdesigners. as for graphics, flash have simple and easy drawing capabilities. for advanced techniques, you have to rely upon adobe photoshop, fireworks or similar softwares.
for sound, someone else may help you.