Hi Jobo,
I was diagnosed with AIH in Jan 2007. I completely understand how you felt with all the steroid side effects, been there done that but I remained working as I refused to stay home to think about it. Everyone at work was very supportive through all my personilty and physical changes.
Are you seeing a hepatologist? I'm assuming you are still on the CellCept (mycophenolate mofetil)? What dose? As you wean from the prednisone (I am currently only on Azathioprine--fully weaned off the steroid in Dec '08) make sure it is extremely slow and that all your LFT's are normal. My final wean from 5mg to zero took 2 months. I dropped 1mg every 2 weeks and went for lab work right before each drop to make sure I could continue with the wean. Oh and before I started the wean, my azathioprine was doubled from 50mg/day to 100mg/day. How often are you having your bloods drawn? Is your doctor planning on increasing your CellCept? That would depend on your current dose though. Don't worry about a flare. I know it's easier said than done. I worry about it all the time but not so much that it affects what meds I take or how I live my life. If your doc thinks you can come off the prednisone, then try. They will monitor your lab work closely after the final wean and if you start showing an increase, then yes, they will put you back on the pred but probably not at the 80mg you started at the last time.
As per the pred weight...it eventually comes off but you do have to work at it a bit 
You mentioned osteoporosis...are you taking calcium supplements? You should be (and should have been this whole time) with being on long term prednisone. I have osteopenia but the docs are only watching it as it hasn't changed and may have been there before the pred use. So I take a multivitamin (very important for liver patients) and calcium with vit. D. As with any over the counter medication, please check with your doctor.
Please post more and keep in touch!