You've got a couple of options
Export all the images as a catalogue, remembering to include the "negatives". This copies everything including the images, thumbnails and catalogue details to a set of files which you can then "Import Catalog" . Only drawback is it takes some time..
The second method is to copy the Lightroom data from the old machine and reinstall it on the new one. Not difficult.
First load Lightroom onto your Mac
Now on the old machine locate the Lightroom catalogue files. They are in <user> Pictures/ Lightroom. Now simply move them to the same location on the new machine.
Once done copy the images to their new home. When you start Lightroom it will ask you what catalogue you want to use. Simply navigate to your catalogue and click on it Lightroom will now use this as default. If you get question marks on the images, it means that Lightroom has lost track of the image files. This can happen if the new location is not the same as the old. Simply right click on the root folder and select "Update folder location"navigate to the new location of the root folder, and Lightroom will update everything automatically.
Don't delete anything until you have confirmed everything has gone well. Then back everything up.
It's not difficult I've done this several times when moving computers and it works well.
One point, you may want to get a network crossover cable and transfer images this way. beats using most other methods
