All of the following assertions, are, of course, subject to dispute. If I have covered anything discussed by a post I might have missed, I apologize for the redundancy.
1) Be bold, not subtle. Bright, primary colors. Texture is also key. Silver Age is characterized by "streamlining" with the advent of new fabrics like spandex, lycra, polyester, etc. In contrast, Golden Age heroes had to make do with older fabrics, layering (briefs over longjohns), bulky tech, combined with normal-style clothing (trenchcoats). The Silver Age costume look tended toward being streamlined tights and simple costume elements, because artists were being pushed for faster turn-around overall. Again, mystic types were the exception, since they were anachronistic simply by virtue of having magic as the source of their powers. Armor was futuristic rather than archaic. The Golden Age buckled their swashes as "adventurers", so flared boots, opera cloaks, and turned gloves edges were favored. Of important note is that anything vaguely alluding to juvenile deliquency was banned (sunglasses, motorcycle jackets)
2) Heroes of both eras wore masks, with few exceptions. Golden Age-style efforts to conceal one's identity manifested as cowls, hoods, helms, archaic helmets. Silver Age heroes preferred domino masks, full face stockings or helmets, partial cowls and helmets, tiaras, crowns, or elected no mask at all. Moderate to excessive facial hair was discouraged as "sinister", unless the character was a mystic type; female heroes wore their hair loose, usually shoulder-length (shorter hair revealing the back of the neck was scandalous; close-cropped would have been considered gender-bending). Pre-teen sidekicks, wearing outfits paralleling that of their mentors, with the boys wearing short sleeves, shorts or briefs, baring their legs almost as often as the girls (that's what *I* noticed, anyway). Teenage heroes in their own right didn't appear until the Silver Age.
3) In terms of origins as they impact appearance, there was a preponderence of heroes whose powers and abilities were mystic. Science, extraterrestial, and tech-based heroes didn't start appearing in force until the 1950's (the age of Sputnik), while mutant, ethnic, and radioactive-spawned heroes made their debut during the 1960s. Therefor most Golden-Age heroes fit the basic human phenotype physically, but appearances started to get exotic when the Silver Age hit.
5) Codename ideas: Golden Age heroes, usually a pair of words strung together, prefix/noun (Dr. Quantum), military rank/noun (Lieutenant Blitz), or adjective/noun (Green Gardener), or noun/gender (Turnip Woman). Silver Age, less so the noun/female gender and the rank/noun formats because of the women's lib movement taking place in the latter part of the period, and anti-war sentiment. Silver Age started the trend for one-word codenames without being preceded by "The."
That's all I can think of. Can anyone else spare a couple of suggestions on costume design?
Edit: I left out something about patterns on the costume. I'm not talking the chest detail. Aside from "racing stripes", any of the other patterns you see available on the costume creator are probably best left off if you want to keep within the theme. Plus, if it wasn't implicit before, matte versus sleek surfaces for more of an authentic look....and you can't go wrong with lots of yellow. :)