More decisions! How do you want to connect the links? How you connect the links is up to you. Something to consider: Since I chose not to solder the jump rings closed, I decided to use brass jump rings because brass is stronger than copper and less likely to pull open. Nickel silver jump rings would be a good choice as well.
The interior diameter (ID) of jump rings that should be used to connect the links will be determined by how far in from the edge of the link the holes are. Even though they hold the links closely together, 5mm round jump rings are pretty large looking. They will work if you solder them and then squish them into oval shapes with flat nose pliers. Purchased oval jump rings are a great option as well.
Smaller links in each of the link corners can be connected together with another jump ring. 18 gauge jump rings, the smallest gauge that should be used as a single ring, may not have enough "presence" for your liking. Up to 16 gauge jump rings will fit the holes. Using larger size rings between the links to connect the jump rings in the link corners can add length as well as design possibilities. Try using twisted square wire jump rings.
We each will have our personal preferences. I happen to like the look of two 20 gauge 3.5mm ID jump rings in every link corner as well as for connecting the corner rings together.
Another option: Use slightly larger jump rings in the corners and connect all four of them to a larger heavier gauge jump ring between the links.