a few things of storm of swords i don't understand

[bloodsteel bitterraven]

following the battle of black water bey Why are'nt the lannisters and tyrells attacking stormsend. why are they not pursuing stannis since he's in such a weak position with all his army destroyed.

I am guessing it's because they have more urgent matters? We'll see what happens later.

when stannis uses gendrys blood and throws the leeches in the flames, why does he waste his wishes on robb stark and balon grey joy, people who are not a direct threat to him, he could have used the same wishes to take out tywin/cersei/mace tyrell.

Good question. He could also used the leeches to kill Joffrey, Myrcella and Tommen. His reasoning was that he wanted to kill the usurpers. If a new usurper appeared, he would deal with him/her then.

[w/Fire and Blood]

We have no bloody idea what dragonglass can do to wight, or fire against The Other. Because we didn't see that happening. There are one scene when they're trying to use torchwood against the Other but he's too quick for them to properly burn him.

Actually, in one of Samwell's chapters (I think when he's talking to Stannis) he mentions that he tried Dragonglass against a wight and it just shattered. Mel tells him that they aren't the true enemy, but just a tool of the true enemy (The Others).

[Hos the Hostage]

its quite fustrating we never able to see jons reaction to the red wedding.

This is all you get as Jon's reaction, and for me, it does convey a deep sorrow with so less words:

Samwell POV, A Feast for Crows:

Jon smiled a strange sad smile. "And pull your hood up. The snowflakes are melting in your hair"

Jon POV, A Dance with Dragons:

The cold trickles on his face reminded Jon of the day he'd bid farewell to Robb at Winterfell, never knowing that it was for the last time.

"And pull your hood up. The snowflakes are melting in your hair"