Batch photo tagging in Lightroom Classic CC

I shoot landscape and professional models, so my photos are organized by date in folders. I import in place and save from Photoshop into folders that are either by model/job or by location.

I don't use either keywords or collections. So yes, you can do what you want. Its easiest to organize folders first then import in place but you can certainly move things around within LR.

You don't, or you do it the slow way by dragging and dropping them.

Keep adding keyword tags and put your time into doing that. Remember too that a photo might contain more than one person, which works fine with keywords but not when you try to use folders. So add those keywords, and use collections and smart collections to have folder-like groupings.

Use folders simply for storage and physical security (ie backup/restore) of your images, keywords and other metadata for categorising what's in them, and collections for collecting and gathering.