Wall of text time!

My personal recommendation is to go for the Amethyst or the Bent Graduate - basically the same toy, just with different colors. The Bent Graduate was my first glass toy, and it's still a loved resident of my toy box. It's not very big and you get to try out a couple different features: smooth or textured, curved or straight. Always be gentle when using glass toys. They're completely rigid, so if you're too rough you can hurt yourself. Because of this rigidity, it's a good idea to go a little smaller than you would with a soft toy.

Taking care of glass is a bit more involved than some other materials, but it's nothing huge. Make sure the toy is protected from scratch damage in some way (wrapping it in a shirt, using a special bag, etc.) and impact damage (padded bags can help, but really the best bet is to just be careful not to drop it). Always inspect the toy for scratches or fractures before use, and don't use it if you see any. You can clean glass toys with soap & water, toy cleaner, by boiling, bleaching, or putting them in the dishwasher (top rack, no detergent).

I don't really do any temperature play, but I've heard using a bowl of warm or cold water is the best bet, especially if you're just starting out. You could use the freezer, but you have to be careful not to leave it in there for more than a few minutes, and don't use the microwave (this can product hot spots that could really hurt you). And never go from one extreme to the other. Pyrex glass is very strong, but rapid temperature fluctuations may cause it to shatter. less