Ok, let me go through the items you are wearing:
You don't have much of a choice there, since it's most probably your only costume with the matching type.
The F rank tiara you are using is pretty much the worst choice you could have made. It has a very low appeal score, and the skill on it doesn't do anything, since your costume doesn't have a burst skill. Use whichever of your headpieces has the highest appeal score. you can ignore the skills on them, since there aren't items with a useful skill if you don't have a burst skill on the costume.
Yet another bad choice. The accessory has +20 omoide as skill, which is pretty much useless, especially since there are much better skills available. It might have some limited use on a solo event, but since this isn't a solo event, you get way more points out of the drive duo skill (ドライブデュオ). Among your items with that skill, pick the one with the highest appeal value.
Arms are usually the slot for the charge level 2 skill, but since you don't have a burst skill on your costume, there is no point in using that skill. So pick whichever bracelet has the highest appeal level. Chances are, that the one you are wearing has the highest appeal, due to the appeal +20 skill. For the Keep Out 4 event, you will want to use an item with chain bonus 100 here though. You can get one by ex clearing the first event of the いつまでもこのままで DL live.
In general, you have made a good choice there with the chain bonus 100 skill. However, by ex clearing the first event of the アナタとノクターン DL live rewards you with an item with chain bonus 150. You should go and get that one. For Keep Out 4 you should use an item with drive trio (ドライブトリオ) here, preferably the one with the highest appeal score.
If you do this while using kiramekirari on master and with a high rank while having 5 hearts, you shouldn't have any issues beating keep out 3 and 4.
Please also have a look at the guide i wrote on gamefaqs, it has a section on skill setups and when to use them:https://www.gamefaqs.com/ps4/730583-the-idolmster-platinum-stars/faqs/74300?page=0#The%20Best%20Skill%20Setups%20and%20When%20to%20Use%20Them
If the guide is too complicated to understand then please let me know where the problem is, so i can improve it.
And while i'm at crosschecking with the game, i quickly checked the other items:
Held note support (Z): 3 (or 5 in the Z case) times you are not punished by not holding a note to the end. As explained above, target support Z has the same effect, although through a different mechanic, and it isn't limited to just 3 or 5 times.
chain support (Z): up to 3 (or 5) times, a bad won't break your combo. Since target support Z turns bads into goods, it has the same effect through a different mechanic, and it isn't limited to just 3 or 5 times.
burst support: A normal doesn't end the burst mode. Since target support Z turns a normal into a good, it has the same effect, although through a different mechanic (i reapeat myself here), and it even works with bads.
And then there is the normal target support, which turns bads into normals, which is obviously inferior to target support Z.
So target support Z has the same effect as all other items combined, and even in a stronger version than every one of them. Yes, it costs more (1000, compared to 500 for chain support Z and held not support Z, or 800 for the burst support), but the cost is neglible, even more so if you just consider the difference. Target support Z is the only item you'll ever need once you have unlocked it.