There is an excellent guide to migrating from Wordpress to Ghost on Ghost For Beginners so this is intended to supplement that rather than replace it.
These tips assume you've already exported your Wordpress comments into Disqus.
Running Ghost on a different domain
I initally imported my Wordpress posts into a test install of Ghost in a local VM and none of the comments showed up in Disqus. Disqus supports several options to mirage comments between different domains. The obvious choice would perhaps be to choose domain migration, but as Wordpress adds the dates into the URL and Ghost doesn't, I thought it would probably be safer to go for the URL mapper. Disqus will email you a CSV with a full list of URLs so it's quite simple to adjust them to the new domain as well as removing the Wordpress dates. It's also quite easy to automate this process in Excel using string functions.
Using a different email address on Ghost
Since installing Wordpress I've changed my email address. My new email address actually shares the same mailbox and Gmail account as my old address, but Disqus doesn't know this. Unfortunately there doesn't appear to be a simple way to solve this issue in Disqus (multiple email address support would have been the preferred way) and my comments from the old blog appeared like an anonymous poster.
I took a bit of a gamble and changed my Disqus email address to my old address; this will only work if you can still access your old address, as verification is required. Fortunately this didn't cause any issue and the Disqus merge tool was able to locate all my blog comments, as well as one or two comments on other sites that I had posted on and merge them all into my account. Once comments have been merged into your account any further changes to your email address are automatically applied to all comments, hence after merging the only requirement is to revert the previous email address change.