Release 1 is the first version of the headset which leap motion open sourced in 2018. Since then there have been multiple revisions to make the headset stronger, easier to print, and more comfortable. For a detailed writeup of the changes made in release 3, check out the Release 3 Documentation.
The leap motion was designed to be able to support usb 3.0, however it currently only utilizes usb 2.0. This means you can use a standard usb micro-b connection with the sensor, which is useful for integrating it into smaller form factors, like an hmd.
Yes! The optics bracket will fit, you may have to rotate it a bit to fit properly on the build plate, here's a screenshot for reference. You can see as noted in the image that the dimensions of the optics bracket with a roughly 22 degree offset are (X:224.14mm , Y: 140.51mm, Z: 101.03mm).