I think it's best to start with the saddle position relative to the pedals. First make sure the height is the same. (are cranks the same length, pedals similar, cleat position?) Next tackle for and aft. KOPS is a good starting position for most people (mythbusters are full of it). If the OP has a bike that they are comfortable on, start with that. Best if you have someone to help. Sit on the bike in the saddle where you ride most of the time. Take the KOPS with a plumb bob. Note whether the string goes through the spindle, a little in front, a bit behind, etc. Now get on the new bike, and move the saddle until the plumb bob is indicating the same position. When that matches, then, get your handlebar position sorted out.