Well, I think your zodiac sign deals with elemental magic more than any other type, since the zodiac signs are basically elemental personalities. So it may make your magic stronger dealing with your certain type of element. But, in general you can do any type of magic and get the same effects or even stronger.
Some signs may be more inclined towards magicak work, but you in no way have to be a particular sign to practice magic. In fact it has nothing to do with your practice of elemental magic either. We are all made up of the four physical elements, empowered and given life by the fifth element of spirit. If you want to be successful at magic you have to be comfortable with all four.
The zodiac does give you an idea of your strengths, the influences that are effecting you and the ways you can improve.
Depends on the person. Some people believe the moon phases effect magidc as others say planets do. Planets go with the zodiacs learning astronomy and astrology can be a great thing to know if using the energy from it. There are oils you could make during the sun sign or moon sign of a zodaic.
The thing you have to remember is that a sun sign (which is what most people go by) is only a small part of the larger picture. The Tropical Zodiac (or any) maps out the celestial energy that was present during your birth. As with Tarot cards within different spreads, or palmistry, you have to take in account all of the aspects in relation to the others. It's not supposed to govern your personality. Rather, it helps give a different, indepth look into a person. The deeper you go into astrology (or any other divinatory method pertaining to one's self), the more accurate it gets most of the time.
If you have your correct birthplace & birthhour get a free natal chart at www.astro.com/ then look at the elements in your chart,
next to the planets you see the signs, I have noticed the elements I have the most of in my chart are the ones I like prefer working with for spells.