Given the small size of strakes I doubt they will do much for combating roll. They won't hurt to fit though if it's a planing hull but they are usually fitted on a model for the look rather than any performance benefit. Chine rails on the other hand are very important as they dig in on turns and towards the bow they act as spray rails and keep the deck dry.
As for layout it depends on the size and shape of the hull. Back from the bow it's best if they run parallel to the keel and can be run all the way to the stern or stop short. At the bow they can be positioned as you say to look right.
Couple of shots of my Faireys. One with the strakes full length and the other one stopping short as per the full-sized boat. I prefer them full length for the look and have done that on all my other builds.
Having Googled the Aeronaut Jenny I see that the beam is quite narrow relative to the length which is likely part of the problem.