How do I display a summary page after finishing a multistep form?
Multistep forms are pretty well documented in Examples for Developers module. Basically if you need a summary before posting, add one more step, as steps have access to values from previous ones. If you need a "thank you" page, use usual redirect. That's the answer for question in title, at least.

If you are using some modules than stops you from doing it the traditional way described above, you need answer from someone familiar with that particular modules. Sorry, cannot help you specifically with ctools wizard.