I disagree with the head accessory, there are only 3 reasons to use the F rank tiara, especially if you have the S rank tiara:
1) You are using quintet burst or certain solo bursts, basically, you need charge lvl 3
2) You are using the hand accessory with 100 combo bonus from one of the DL lives (No. 105) This option actually has the highest scoring potential
3) Your F rank tiara has a level of about 40
Other than that, you end up with a higher appeal when using the S rank tiara and some arm accessory with charge lvl 2.
I can't say anything about the costume since i don't know what type the event is, but the costume you are currently using is bad for scoring, i'm sure you can find something better, but make sure it matches the event (look out for the smilies)
But use arm accessory 105 to get the 100 chain bonus. Pair it with the F rank Tiara (No 1), No 24 for the body and No 47 for the legs.
This way you have charge lvl 3, 100 chain bonus and trio memory appeals, so you have all the scoring skills you can get from accessories, the rest depends on the costume.