Our B&G was 4 1/2 months when we brought him home. He was fully weaned. I did feed him oatmeal a few times because I was concerned he wasn't eating enough pellets. I also soaked a few pellets in apple juice to soften them. Just remember not to leave the juice soaked pellets in the cage very long. You can also try a scrambled egg.
As far as the biting and lunging, we never had that issue. Our breeder was 5 minutes from our house so we visited him a couple of times every weekend. So over the couple of months waiting for him to wean, I'm sure our visits with him started our bond early.
Just be patient, spend alot of time around the cage. Talk, read, sing to her. Hopefully someone with alot more experienced will have more help with how to start getting her out of the cage. I'm only concerned that with the big birds you can't give them their way, they have to know that your the boss. So you have to be able to remove her from her cage, especially at such a young age.
On a good note, once you get everything smoothed out and get comfortable handling her you will see how wonderful macs are. We love ours so much, he makes us laugh everyday.