Hi there, friend ! Great topic !

From my plethora of failed friendships, I can certainly tell you what doesn't work My record of friendships was best described by Benjamin Franklin ... "I didn't fail; I just discovered a 1000 ideas that didn't work."

Q - How much information should a friend be given about my mental illness?

Like Trippin said, this really depends on the friend. Is (s)he informed about mental illness in general ? What attitude does (s)he have towards mental illness ?

If (s)he is ignorant and/or prejudiced towards the subject, and this is a highly likely scenario in this world, you should definitely not discuss any details with him/her. "A little knowledge is dangerous." I've found that telling ignorant people about mental illness only has bad consequences ... they may start distancing themselves from you, they may act differently around you, they absolutely unequivocally will place you in their mental basket of "abnormal people". You will no longer be the same person to him/her, and your relationship will have, forever, changed.

On the other hand, it is possible to divulge to the friend that you're struggling, but utilize vocabulary that they can relate to without going nuts themselves. You can, perhaps, describe your symptoms in layman's terms ... I find it hard to get out of bed, I don't have any energy, I don't feel like going out, etc.

Another point that I've shared with you in the past is that you shouldn't totally identify with the label that your diagnosis is. "PTSD", "Bipolar", whatever. Those are artificial man-made constructs to help with a potential treatment plan. But, outside of therapy, they have little significance, in my opinion. You don't need PTSD written on your forehead when you talk to your friends. It will only hurt the interaction, in my opinion, unless your friend is someone with the background necessary to relate to the labels.

Q - What is appropriate behavior when I am manic/depressed -
do I honor plans made no matter how I am feeling?

Again, this needs to be worked out with the friend. Make it clear to your friend that, there will be times when your energy level is low. The smoothness of the interactions will depend on things like trust and understanding.

Q - Do I go through with ideas that seemed doable during mania that might not be entirely possible when I sober up?

I think this is a very specific Bipolar question. Since I don't experience such polarities, I can't really answer.

As for the other questions, my answers will have the same general tune - share if the person is trustworthy and able to relate to the content (and it's format) you share.