Because of their inherent stiffness, aramids tend not to be resilient and don't deliver much feel or power, though they do hold their tension exceptionally well. For chronic string-breakers, hybrids are a good value. These are rough surfaced strings designed to grab the ball better. The feel or durability of the strings are not necessarily improved. Strings can be purchased in large reels for stringing at home for less.
Larger numbers mean thinner strings.
Thick strings have less resilience and feel than thin strings but last longer. If you're unsure, choose a tension that is halfway between the manufacturer's ranges. You can then adjust up or down until you find the tension most suitable for you. Higher tensions will probably cause a little more damage than lower tensions. The higher the tension, the more boardlike the feel.