"The Secretary of State's Office released statistics showing 3,146,418 Arizonans registered to vote in the 2010 general election; 486,697 people registered in Pima County. Of those, 151,502 people registered as Democrats, a decrease of about 4 percent from the 2008 general election. Republicans account for 142,730 registered voters, a number that increased over 5 percent since 2008."http://www.kvoa.com/news/voter-registration-down-in-pima-county/
More than enough to get the job done.
You need petitions signed by 90,078 voters by my calculation. JLS, you're dead on. 25% of votes cast in his last election.
Also once the petition is filed with the State, there are 120 days to secure sufficient signatures.
Recall requirements by State.
The replacement election is held simultaneously with the recall in AZ - similar to California.