The key to choosing open vs. closed should depend on the rules of the club/track you run with. Open faced helmets are always allowed for autocross. However, track days are more strict and sometimes only allow closed faced helmets. For that reason, I chose to go with a closed faced helmet even though I have only done autocross.
Helmet fit is the next most important factor. There are many measurements you can do on your head to figure out what size is right for you. Saferacer has a good guide and is a good online store to racing equipment from. Nevertheless, your best bet is to find a local race shop and test on helmets there, especially since you will be wearing glasses. You will be able to figure out size, fit and comfort the best that way.
I don't think color matters.
Higher end helmets will be lighter weight and have better venting to cool your head.
Chin straps shouldn't matter as the strap should always be loose enough for you to be able to open and close your mouth. You're not ratcheting the strap onto your chin.
In the end, I listened to none of my advice besides my first sentence. I bought the cheapest SA2010 closed faced helmet I could. I ended up with a Zamp helmet for $150 (I think) and have no complaints. It fits and protects my head and that is all I need it for. I didn't consider venting, color or comfort. __________________ 
2000 M5 -> 1996 318ti -> 1997 328i 
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