Since a good deal of netdata's value is in keeping its' footprint as small as possible, and instances are stateless, adding default limits for child pods seem to make sense. I would include parent and k8s-state too, but AFAIK those are relative to the size/complexity of the cluster and therefore hard to predict.
Setting resource requests is just good practice. Setting limits prevent runaway processes.
Based on the docs I suggest defaulting the child to
resources:
requests:
cpu: 150m
memory: 200Mi
limits:
memory: 250Mi