Okay so here's my take:
Yes he wanted to fulfill Ra's Al Ghul's destiny, but that's mostly because he had idolized him. I don't think it's weird that he had some vendetta against Bruce. Bane was kicked out from the League despite his great respect for the organization whereas Bruce was the opposite. Bane greatly hated Bruce because despite being taken in by the League (and considered to be Ra's Al Ghul's greatest student), Bruce had rejected them at the very end. If anything, it makes sense in that it's his true motivation for even plotting to take over Gotham. Unlike Ra's Al Ghul who saw it as some form of true justice, Bane actually recognized himself as a "necessary evil".
I always considered Bruce to be a part of Batman, so I was pretty satisfied with what we got but that's just me.
Bruce isolated himself for 8 years. By the time he researched about Selina, it's readily assumed that he only found out about her at that point, in which he discovered that she was a pretty experienced cat burglar.
The plan was NOT to kill Bruce in the city with the bomb, the plan was that Bane would capture the city to torment Bruce by showing the pathetic state of Gotham. Through his rule, he would give hope to the masses while secretly plotting to actually blow them all up as a way of mocking Bruce for his supposed failure. When Bruce had escaped, Talia had no choice but to speed up the bomb's detonation despite the fact that Bane had initially wanted to prolong it (it was meant to go off a few months later I think). While it's never disclosed if they were willing to blow themselves up along with Gotham while Bruce was stuck in the Pit, I'm still pretty sure that Talia and Bane were twisted and dedicated enough to willingly kill themselves like that.
