The icicles for because of differences in temp. Which you may already know. All your attic ideas will work just fine. Just remember to leave the insulation a one inch space at the bottom roof deck for the ventilation to work when you install the soffit vents. They do make a material called prop a vent for this purpose. As for the chimney, I would wait to see what happens with the other improvements. You may not need it or it could change the dynamics altogether. I always do one thing at a time , and see how that works so I can narrow the problem down.
Good luck, now is the time to insulate before it gets hot up there.