Migration to OpenPublic from existing D6 site

I have a project that involves migrating an existing Drupal 6 site to Drupal 7/OpenPublic and wonder if anyone has experience or advice on doing this. I'm trying to figure out how to sequence things. Should we: (1) set up a fresh OpenPublic install and then import the content, or (2) First upgrade the content from D6 to D7, and THEN add, enable and configure the OpenPublic modules? How do we handle conflicting site architecture between the current site and OpenPublic?

I think there are three ways to approach this, which I'm going to try in the following order:

(1) Run update.php from D6 to D7 directly on an OpenPublic codebase.

This approach essentially involves the following steps:

1. Take a version of the current running website and disable all the modules on it except for CCK.
2. Overwrite the existing codebase with OpenPublic. Then, rather than run the installation profile, run update.php.
3. Use the content migrate module to update the existing CCK fields to Drupal 7 Fields.
4. Manually go through the steps that are coded into the OpenPublic installation profile and turn on its features and configuration settings, or else write a script that essentially mimics the steps in the installation profile.

(2) Run update.php from D6 to D7 on a plain-vanilla D7 codebase, and then add in the OpenPublic code and configuration.

This approach would go as follows:

1. Turn off all the modules on the D6 site except CCK.
2. Install a plain-vanilla D7 codebase and do the CCK to D7/fields migration.
3. Add the OpenPublic custom code, and then manually turn on its functionality instead of running the install profile.

(3) Run update.php from D6 to D7 on one codebase; set up a 2nd, OpenPublic website; and migrate content from the D7 site to the OpenPublic site.

This approach would go as follows:

1. Turn off all the modules on the D6 site except CCK.
2. Install a plain-vanilla D7 codebase (which I'll refer to here as OLD7) and do the CCK to D7/fields migration on it.
3. Set up a separate, fresh version of OpenPublic (which I'll refer to here as NEWOP).
4. Migrate content from OLD7 to NEWOP by either using the backup and migrate module or by using the Services API to serve content from OLD7 and retrieve it on NEWOP.

One of these migration strategies will work (hopefully the first one, which would be the easiest). Any advice, anyone?