1) Is backstory considered bad novel writing?
I've heard that it's frowned upon but sometimes it can be necessary for the plot, if done right. For instance, if you overdo it, the action isn't 'here and now' anymore - and the readers sitting there getting impatient for things to keep happening with the story itself, not the backstory. However, sometimes backstory is needed, or else the reader will sit there and wonder what the hecks going on. Or if they find out through dialogue something horribles happened that's relevant to the plot, backstory can be a better technique simply because, as readers, we like to experience the horrible misfortune rather than simply learn about it afterwards.
In short, I'd stick to what works best per book. If you choose backstory, break it up. Make it short and sweet and relevant when needed. Don't rely on it as a crutch to fill 'dead air', when your plot has stalled - this may be obvious to some.
If I were you, I'd inject the back story at the best moment to do so, when it would have the greatest emotional impact. And maybe if being hit with, say, a memory, use it when it would have the WORST impact on the characters life at the time. As an example, the lead is getting down and dirty with someone, and its important for them to do so, when they're slammed with a backstory that ruins it all, making the plot have more obstacles to overcome than before.
2) Much of my story happened in the past, which leads up to present day. How do I bring it current without going into the past?
I don't know the details of your story so I can't give straight out concrete advice here. It may require restructing all your scenes, or else just messing around with some, backstory, prologues, etc, etc.
3) Should my main character tell what happened in the pass to another character or the reader?
This can be a very helpful tool. If it fits, use it.