I have been through the process a few times. Also being a neighborhood leader I have been a part of many, as far as being for or against.
The first thing I would say is look around at what you have, and how it looks. Does your house need paint, siding falling off, dead trees standing or down. Every neighborhood has that guy that wants more, but does nothing for what he has.
Next. How do you get along with your neighbors. Likely they will have a say in what you will be able to do. If you do not know them, go meet them. If you do know them, explain your intentions. Get some feedback as you talk to more neighbors. Before you talk to them, figure out exactly what you want, and do everything as to not changing the plan.
I have had projects pitched to me, that when I first heard about them, I did not ever think a good thought about, and ended up I was all for it. I have also had what I thought was good ones, that just were not all that great when I learned more. Usually neighbors so many feet away will be noticed by the town. The town will want feedback from them. You need to talk to them about your project, because that notice may not sound like anything you are trying to accomplish.
Proof of hardship is the hardest to justify, and is usually a requirement for any board of adjustment. I have seen something as simple as a race car and trailer being enough.
One other thing shoot for the moon and figure on settling for less. Many times they will work with you some. You may not get what you want, and they may not get it either. Some where in the middle will work for both.
Talking to the building department is the best. At any hearing that you will have, they will likely make a recommendation of passing or denial. Figure out what side you will be on. If they are on the passage side, you may not want to say much during the hearing. If they are for denial, you had better plan on taking all of your allotted time, and maybe the wife too, to address the problem areas.
Last but not least, unless there are other metal building very close to you, you likely will not get a metal building. Seriously who would want one in your neighborhood. If you want a larger garage then you should be able to make it blend in with your house and neighborhood. You would have to really show me some hardship to get a metal building.