How to upgrade / convert from Lightroom 3 to Lightroom 6 Between Two Computers

Hello!

I'm confused about the different directory structures under Windows between LR3 and LR6 to ensure I get everything copied from the old machine to the new one and minimize issues in LR6.

THE FACTS

1. I am not a user of Lightroom.  I installed it for my wife and she's the "power" user in the family.  But that's going to change.

2. Moving from LR3 to LR6.  Leaving LR3 behind on an old machine, moving to a fresh install of LR6.14 on a new machine.

3. All photos are stored on an external 4TB drive.

4. The Old Computer: Dell Inspiron 545, Win10 Home 64-bit (upgraded from Win7), 2.5GHz, 8GB RAM.  All updates current.

   --My account is "C:/Users/Mark (Admin)".

   --My wife's account is "C:/Users/Jambalaya".

   We don't share LR3 on this machine.

5. The New Computer: Dell XPS 8920, Win10 Home 64-bit, i7-7700 3.6GHz, 24GB RAM.  All updates current.

   --My account is "C:/Users/mlbra".

   --My wife's account is ""C:/Users/jmbra".

6. I located and copied the catalog file "Lightroom 3 Catalog v1.lrcat", and the folder "Lightroom 3 Catalog v1 Previews.lrdata" under her account.  I've placed these on the new machine under "D:/Lightroom Files".  These were under my wife's account on the old machine but I want both of us to use the catalog on the new machine.  I'll open LR6 and point it to this catalog instead of the default created at install on C:/.

7. From reading the forum and elsewhere, I need to also copy the CameraRaw and Lightroom folders to ensure presets, profiles, templates, etc. come across to LR6.  On the old machine they're under:

   --"C:/Users/Jambalaya/AppData/Roaming/Adobe/CameraRaw"

   --"C:/Users/Jambalaya/AppData/Roaming/Adobe/Lightroom"

And here's where the confustion sets in...

1. The folder structures for "CameraRaw" and "Lightroom" don't match between LR3 and LR6.  Do I just overlay LR6 with the LR3 folders from the old machine?

2. Given that my wife and I want to share LR6, do they go under her account?  My account?  Both?  Or on the D:/ drive somewhere with the catalog and previews?

3. The photo files and previews will maintain the original drive letter and names (so LR6 *should* find them), but under Windows, will the new (different) account names on the new machine screw things up?

4. Is there an order to doing this to minimize issues?  Do I ensure everything is moved before opening the LR3 catalog in LR6?  Or do that first and then move these two folders?

The only thing I've done at this point is to copy the catalog and preview data to the D:/ drive of the new machine.  I've opened LR6 pointing to the default catalog.  That's it.

Hope this wasn't too much or tool little detail to go off of.  And hoping someone can help me through this.  It's not as straightforward as I was led to believe...

Thanks much,

--Mark