Hey dude, I can tell you already that you are going into a big topic that is going to need to be broken down. I cannot offer precise sources because depending on what you are looking for, your sources are going to differ wildly. However, I can offer you a methodology to get started:

1. You need to go in with the right mind-set, these are not "costumes" per say, but material culture or clothing because the people that originally wore them did not treat them as "costumes". These were items that people chose to wear for a variety of reasons suited to their own needs/wants.

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2. This is a huge topic, that you are going to need to narrow down to a pretty narrow band because people will vary their clothing based on their location, season, social class, gender and profession. You can't just say "anything pre 1600" because that still encompasses the whole world and around 5000+ years of human history. Are you a Neolithic hunter in the Lower Indus Valley? Are you a Greek farmer circa the 1st Persian Wars? Are you a Chinese Scholar during the 500ADs? Are you a noblewoman in the Aztec city of Tenochtitlan before the Spanish conquest?

3. The 1st thing you should do now is a pick a culture, and a time period because that already narrows down locations. Then pick a particular social class, gender and a profession. Because people's fashion choices are determined by those factors. The more specific you are the better, because if you are looking for accuracy, that is your best bet. Not going to be easy, because certain things are better documented than others. Nobility, Royalty and the highly educated strata tend to write things down, or have their material culture preserved or documented better than your average lower classes simply because they are deemed more important. Its harder to research and understand lower classes, enslaved individuals and minorities because they do not tend to leave as much behind, or their stuff is not as well preserved.

4. Aim for first, what we call "primary sources": archeological evidence, museum pieces and extant originals are by far the best. 1st hand accounts by people who have been there are also decent, but take them with a grain of salt though, do your homework and take into account the narrator and the bias/agenda they might have. A Roman author describing how Germanic tribes live and dress will have a certain perspective that might not be as accurate to reality. Furthermore, lots of 1st hand accounts, especially by early historians, were heavily based on hearsay/gossip. Still, they retain a lot of value because at the very least, they can inform us as to how certain groups were perceived or stereotyped as.

5. Depending on how many primary sources you have available, you might need to draw more or less from "Secondary sources" a.k.a books and research papers published by accredited historians. While sometimes not as detailed or comprehensive as one may want, they still offer great insight and context into what you looking for.

Not an expert, but I have worked in museums centered around portraying 18th century history for 2-3 years, and currently do a lot of material culture research and garment recreation. If others want to pitch in, and offer a better answer, please do.