Hey Carrie. I could've used lots of advice when I started but just experimented. Here are some things I learned:
Yes, you can add too much fragrance. The wax can only absorb a certain amount of the fragrance oil. For soy candles, the maximum amount you should use is 1 oz. of fragrance per pound of soy wax. If you put to much fragrance it will leak out of the top of the candle and 'bead' around the top. It oozes out and does not look good and its not easy to wipe off as it is oil.
If you pour your candles too hot, the will not sit right in the container. This will matter if you use glass jars. you will be able to see the mistakes/bubbles/white marks/discolorations..etc. Sometimes you can get big holes in the tops of the candles too if you pour too hot. But you can always fix that with the heat from a blow dryer.