Well, if you seriously want to do well in the game, if you just started, I highly advise you spend as many hearts as possible during the event (at least enough to get 2nd SR). The goal is to play as effectively as possible to get enough LP such that you go to sleep without worrying about the game... (I know I was this addicted at some point). During events, you not only get awarded for playing more, but you also can play another song with pts earned from the event, giving more xp, allowing you to level up that much faster.
Also, do not bother focusing on rares since they will be outclassed quickly. Getting 2 SRs is probably the best because for now, both will aid your team, but when you get stronger, you can idolize and make a fairly strong team. (When starting out, it might take 30 hearts to get a 2nd SR, but alternatively, it costs 50 hearts to guarantee a SR)