IME, the biggest thing to pay attention to are the following things:
The amount of gold used in the ring. A smaller band looks more feminine and pretty, uses less gold (which makes it cheaper) but it will also bend easily. I have rather long fingers, so I tend to go with wider bands, of moderate thickness. Part of the decision here is going to be the shape of your fingers and what looks good on you. Also, consider what you're doing while you're wearing the ring. If you're only driving a car, then you can get a very thin band and not worry. If you're going to be more active, you want a ring with a little more gold in it so that it won't bend (it's happened to me before).
Which leads me to the next point--the security of the setting). Depending on what you're doing, you may not want a ring where the stone is set way off the surface of the band (like many engagement rings). Again, this should be part personal preference and part practical-- what are you going to be doing. Again, only driving, it's not going to matter much. If you're doing anything where the stone might get snagged, caught, bumped or whatever, you want to make sure it's not going to get knocked right out of the setting at the slightest provocation.
Good things to check are the thickness of the prongs, if you get a prong setting. Small prongs can break easily, and then it doesn't matter how secure the setting is. Once the prongs are gone, so is your stone. You want to analyze this around the concept of what you're going to be doing while wearing the ring. Small, thin prongs look nice and emphasize the stone well, but won't handle much abuse. Big thick prongs, or a setting that holds the stone closer to your finger will be more sturdy but less flashy.
As far as a replacement/repair program-- for the amount you're spending, it may not be worth it. That's up to you. A better option would be to add your jewelry and other valuables to your renter's or homeowner's insurance. If you're renting and you don't have renter's insurance, I'd really recommend it. It can usually be got for pretty cheap plus you'll get a discount on your auto insurance if you get it through the same place. The auto discount winds up equaling the cost of the renter's insurance, so you basically get it for free. Really. I'm not making this up.
Aside from the left ring finger, I don't think there are any other things you have to worry about. I've worn rings on just about every finger of either hand, though usually not all at the same time. I would wear rings on my left ring finger even before I was married. Usually only when I was dating someone, but that wasn't even a hard and fast rule. Wear your ring on whatever finger/hand you like it best. That's the best rule.
And post pictures! I love jewelry!
