I think a regular shingle roof would be more appropriate for the house. Metal is kind of country and more expensive. I think if you do a garage on the side, the roof line has to stay in concert with the house too.

I like the colour scheme you have. Perhaps the grey siding could be a tad darker. I would look into cleaning the white spalling on the brick, redoing the landscaping, and add a roof or shelter over your front door. It's a pretty house that just needs a bit of tweaking. Also, when the time comes to replace the shingles, go for black or very dark charcoal.

Yours is one of the better looking and nicely designed exteriors that I've seen on Houzz. I like the composition, scale and proportion. If you want to keep shutters on your home I would suggest replacing what you have with appropriately sized operable shutters. It's a bit hard to see in the photo but if your door and sidelights have 80's decorative glass I might consider replacing to update the look. You might even consider replacing the door and sidelights with double entry doors. I would suggest looking at your landscaping - especially thinning out some of the shrubs in front of the porch. Just to say again - you have a lovely home!

the gutters would look so much better in a copper color, especially w/that Jade color. anyway you can get them painted (or don't know if you're getting new ones) you could do the bronze/copper, or a brighter copper, address numbers and copper window boxes (You can order copper sheeting and make these yourself. or just paint a copper color. but the real stuff patinas w/time. I have a roll of super thin real copper. it's not difficult to work with) for the front door, I'd do the jade color, or even a lighter jade. If you don't want green on the trim, How about one of these Bronze colors? for the garage door I think any of the 3 would look nice some other color palettes