Welcome to OCDO and Virginia.
Plenty of OCers in and around Arlington. All in all the Arlington area is an interesting and friendly place to live, though the conservative values are more dominate the further south you go.
Virginia localities are preempted by state law regarding firearms.
For stories/experiences about that area go to:
The magazine restriction that applies is more than 20 rds is illegal if you do not have a permit in larger metropolitan areas - they are specified.
Sign up for the free Va-Alerts and do consider joining VCDL, the premier supporter of RKBA and self-defense in Virginia - "Defending Your Right To Defend Yourself"