ok, the lenght of future path, you see changing constantly and this is because it is showing the future, IF all other bodies are suddenly frozen forever. because they're not, the future path line is often inaccurate and wiggles around. THus, it is worthless to make it much longer than it currently is.
if you mess with the eccentricity enough, you'll eventually get the hang of it and know exactly how the orbit will look, it just takes some practice imo.