Finally bit the bullet to migrate to Lightroom. As per instructions I generated full size previews, quality level 12. The Aperture library (managed) had about 3000 photos and used 43GB. After generating the previews the library had grow to 65 GB. Is that to be expected. The new Lightroom master file for the 3000 photos is 41GB. The .lrcat file is 32MB and the .lrdata file is 270MB.
The photos ini Lightroom, are they the original photo, edited photo or both from Aperture. Anything else I should check before migrating the remaining 200K photos.
I should probably regenerate the Aperture previews to half size and a lower quality to recover disc space. If I don't I will need close to 2TB for new Aperture previews and 2 TB for Lightroom photos