--> "I will move on to LRCC. My photos are on an external drive."

No. Don't do that. Take the subscription and use "Lightroom Classic". It will have the workflow you are used to and will automatically update your catalog without destroying your old one.


---> " any editing becomes saved in the new catalog which can only be interpreted by LRCC."

Lightroom CC is a new more "mobile" editing program. You will get it with the subscription but it will be a major change to your workflow. As you move forward with the subscription you will find good ways to use Lightroom CC with Lightroom Classic.


--> Can I install LRCC on a second computer? How do save a second copy of the original catalog? CC is the non cloud version

Lightroom CC keeps your images on Adobe Servers. Therefore you can work with them from as many devices you can find that are connected to the internet. Lightroom Classic (like the one you are used to) can be used on two computers. There is NOTHING purposefully built into Lightroom Classic to make it a multi user system. All efforts at that are user invented tricks. One such trick is to put the catalog on an external drive with the photo files but that normally slows it down a lot.

--> "I have never used PS before "

With the upgrade to the current Lightroom Classic you will find less need for Photoshop. But, since it is included in the subscription, it has several things it can do better than Lightroom. My favorite is the removal of ugly tourists in my travel photos.