Thus far you have collected all readily available material. Now some further research should be done. Let us start with the windows. Your information may not be complete or it might not appear to be quite correct. There are a number of avenues to help you out. One is to figure out what the general theme (if there is one) of the windows are. For example, if a series of windows depict the Beatitudes or the Ten Commandments, you may be able to figure out what a window is supposed to be but not necessarily why.
It is a good idea to record all the symbols in a window. Some may have been glossed over by previous persons doing your project. If the artists used traditional symbolism there are a few good references that you might employ to assist you in deciphering the window.
My favorite book is “Signs and Symbols in Christian Art” by George Ferguson. It is very user friendly and unlike many books out there concentrates on Catholic/Christian specifics. It has been in print since 1954 so may have to search for it though my addition was printed in the 80s I believe. Another book is “Saints, Signs, and Symbols” by W. Ellwood Post. While not exhaustive, these books have most of the basics.
There are some excellent websites as well. Seiyaka.com has a lot of great information. Fish Eaters is pretty good, and Christiansymbols.net is excellent.
There are times, however, when these resources will fail you. It might be because the artist has chosen to use innovative symbols that unless you are familiar with the artist’s intent they may confound you. For example, at one parish the windows were depicting the Ten Commandments and artist used red circles to mean “don’t!” Fortunately we came across an old paper that told us of this. (Don’t covet was interesting.) But how would we have known otherwise?
That leads us to your next step if you are desperate (and lucky.) In the corner of one of your windows (assuming they are all made from the same company) there very well may be (usually in the lower right hand corner) the name of the company responsible for the windows. At one parish it was the choir loft window, at another that last in a series in the nave of the church, at St. Sebastian it is in window off to the side of the sanctuary. It might be the artist and his studio itself, or the company that hired the studio to make them and then they stuck their own name on it. In any case this will give you some information. At the very least it will provide some historical data for you. If you are lucky, it might give you everything you want to know.
There was one set of windows that confounded me to no end. The artist was very creative and once you got into his mindset they made a lot of sense – but we needed a key. I found the name of the creator of the windows and then found someone at the company that would sneak out the blue prints for me. I ran down to the library and copied them as quickly as possible along with the artist’s notes. (Can you imagine trying to copy blueprints on 8 ½ by 11 sheets? – the taping together later was horrendous!) But the result was great! All the mysteries of the windows were cleared up and they became great tools for catechetical instruction.