hkpeprah, I think you should be fine with CustomVars as one of the attributes is already available to you -- page dimension.
If you set CustomVar on session or visitor scope, you will have the values for a given test available for all the hits that get sent during a visit (including all the events and e-commerce transactions).
Still I would suggest testing only one page so that you can be sure what changes actually caused any lift/drop in conversion rate. Running multiple test at the same time is not the best way to go (unless you can segment traffic so there is no overlaps, of course).
Hope this helps.