I have a set of arms that currently consist of a 5 lame metal elbow attached to a leather vambrace. The vambrace is circled on the outside by two leather belts and a third belt circles the inside of the top metal lame right across my bicep.

Every time I move or drop my arm, the entire encemble slides toward my wrist. Is this a matter of poor fit, or have I strapped the pieces incorrectly?

Historically, the plates would be tied a arming jacket, rather than attatched to each other.
Other than that, it is hard to get the plates to hang without cutting of your circulation.

English Heritage has a good video that shows the pointing of the arm harness.

Thanks! My arming jacket has points for the spaulders but not the arms. The video does a good job of showing where points were (and weren't) used. The little leather tab on the spauler was nice too. While we are on the topic, does anybody have any good recommendations for cord? My spaulers tend to eat both leather and shoelaces.

I would point to a leather tab, not directly to the metal. Hemp, quality leather lace and linen make nice points while para-cord and thin leather laces do not.

You might want to purchase your first points to get a feel for how they're made.

Historic Enterprises

Warp & Weft

I also noticed in the video that each arm was attached at the rerebrace with two points. Would the leg harness have points as well and, if so, how many?

Thanks! Obviously my self-taught education is lacking: I have never heard a pourpoint before today.