I personally would make a custom bio, but Kabuto and Shikamaru are my favorite characters in Naruto, so I'll definitely stick with them for some time. It's good to be creative though.

My bios are in dire need of an update though.
The best use of a flash bomb would actually not be on a kunai, but direct usage by the hand, or tossed in front of the opponent. In a battle, your eyes can't be everywhere at once, so by simply distracting an opponent and their field of sight can allow you to toss a flash bomb down quickly.
There is also a S-Rank Lightning jutsu that serves a similar purpose, that I am sure you will learn sometime soon.
Remember that there are basically NO restrictions on basic ninja tools (unless they are a simple Ninjutsu), so feel free to use them as much as possible. I will do my best to give you detailed examples and ways to use them during any battle.
The string idea is also great, but remember that a kunai is long and slim, and may not work well with the centripetal force in the air. Shurikens, which I will go over next, are better suited for such an usage, but good thinking nonetheless.
There's one last tactic I love using myself with kunais, and I'll share it with you too.
In battles, there's something called "zoning". This basically means forcing your opponent to go where you want to go because they sense danger coming from a particular side and will react to it.
You can attach fake explosive tags to kunais and also utilize this purpose. Say, for example, I toss a kunai with a fake tag on it toward you and your right side. You would be forced to jump away to your left side, where I have ready another dangerous jutsu, or just some traps.
Keep that in mind the next time you battle.
Okay, moving on.
Shurikens.
You must be registered to see images
Describe to me how they would work and how you would use them in a battle.