Only one of your questions possesses a definitive answer. The other three ('Joan's rights in the army', 'Joan's tactical input in battle', and 'Joan's importance to French victory in the Hundred Years War') are not definitively answerable one way or the other.

I've discussed whether Joan 'fought' in hand-to-hand combat and the definitive answer is no. Did she risk her life 'leading the line' with her army? The answer is a definitive yes. See here for a rather extensive breakdown of Joan's military career.

While Joan seems to have possessed the rights of a French captain (such as the ability to order the execution of a rival captain, and negotiate the return of hostages), she was not extended the rights that would be offered to a male military leader (ie. she was not entitled to be ransomed) when sold to the English by Jean of Luxembourg (who had bought her from a crossbowman in his service).

Whether Joan was a figurehead or an active contributor to war councils at Orleans, Jargeau, and Patay really depends on who is talking. This is really a problematic source issue as our primary source for this information is the Nullification Trial of 1455-56 where the French are actively attempting to paint Joan in the best light possible (for the most part) and thus her 'miraculous' knowledge of warfare must have come from God. See this post for more information on the Nullification record and a breakdown of her trial at Rouen in 1431. Essentially to decide whether Joan actually did have significant input into the practical prosecution of warfare requires a judgement on whether or not you believe the deponents who said she did or those who said she did not.

Likewise it requires informed judgement to decide whether or not Joan's brief career in the service of Charles VII 'saved' France. See this post for the historical context of France in the first half of the fifteenth-century. Is Joan of Arc a pivotal moment or a footnote, it's really just up in the air. I'm familiar enough with Joan of Arc's life to make my own judgements about other 'big' questions for which there is no really definitive non-subjective answer. Take, for example, Joan's 'mission' and her 'voice(s)'. On her importance in wider French history I am not knowledgeable enough to offer a ruling.

For answers about the other issues check out the bibliographies available in the above posts and read them.