You unlock 2 Acquisition (the box currency) each time you level. when you get it just go unlock any component you think will help or just completely randomly pick the items. But either way by Rank 23 you will have collected enough Acquisition to have acquired 50 pieces.
each rank seems to consist of 24,000XP so a good way to earn through that is to play ranked fleet battles which can give upwards of 9,000XP per game at least 2-3 fleet battles (with maybe one or two dog fights) will rank you up. and then its just a case of saving them up and spending them or just spending as you go.