To answer your original question, I would look into FlexiSign for software. We use an older version of Gerber Composer, it works just fine for basic street signs.
I would suggest you buy your aluminum presheeted with whatever sheeting your spec calls out for. There are a few companies that can provide this pretty cheap.
Next I would purchase and cut the vinyl you need for the signs. Like mentioned a clear vinyl (blue, green, etc) would work well over a white pre sheeted sign blank. If you are making white street name signs, just purchase a black vinyl for the letters.
