You can carry openly if you are 18 years old, but not yet 21. Having cash is not a part of Arizona law on open carry, but some police might think it makes your open carry more understandable.
The real risk you have is uninformed or anti-gun police, so I would carry a recorder with you. As you deal in phones, perhaps you have one that can perform this function.
There is the federal Gun Free School Zones law that could be used against you if you are carrying within a thousand feet of an elementary or high school, but I have never heard of it being enforced in Arizona. The first version was ruled unconstitutional in 1995, in Lopez v. U.S., but president Clinton managed to push another, almost identical bill through Congress that year. It has never been constitutionally challanged, which is why I think so few people are charged under it. The federal government does not want to lose a case like this in the Supreme court.
Then again, very few people want to be the test case.
I am not a lawyer.
I think you would want to use a retention holster, such as the Serpa. Others on this forum have found it to be useful.