by North_Wolf
I recommend going for the second core set right away rather then expansions first and then the second core set.The extra dice, overall cost and number of ships really helps. Without a second core set you are also not likely to use many options out of the base set (only a few pilot combos make sense with only 3 ships).
Only after this do I see a need for the expansions (since they add squad building options that are not hugely useful without a higher model count).