How can I reorganise my LR pictures between the different HD of the "storage location for originals"?

On top of syncing online when I can have access to a descent internet connection, I mainly store my pictures (DNG only) locally in an external HD (lets call it HD1) which is now full. From what I understand from previous post here I now have to change the address of the "storage location for originals" to a new external HD (let's call it HD2) to save my new pictures locally. Is that correct?

If so, many questions arises to which I could not get any answer here yet so I try again :

1. When I need to access my older pictures offline will connecting HD1 to my computer make those pictures available even though the "storage location for originals" address is now different and correspond to HD2?

2. Can I reorganise my picture between HD1 and HD2 and move them around from one to the other?

3. If yes how can I do that?

4. If no, will I have to switch to Lightroom Classic if I want to be able to manage my pictures to have control over the HD location of my pictures ?

5. If I have to switch to Classic

a. how the hell can I transfer my LightroomCC pictures to Lightroom classic in an external HD ?

I tried using the sync with Lightroom option and in preferences/lightroom sync I set "specify location for Lightroom's synced images" to my external HD but classic keep saving those files on my Mac hd in Mobile Downloads.lrdata. What am doing wrong? Is this a bug?

b. How can I keep all the editing work done on them in LightroomCC during the transfer to LRClassic ?

I would really appreciate the help as I am completely stuck in my work because of this.

Thank you!