Starting in Bridge

Adding to what Erik said (he's 100% correct on everything), whether to continue with Bridge or use Lightroom Desktop or Lightroom Classic is a choice you may wish to mull over. I use all three, but for different reasons. Let me elaborate.

Bridge, as Erik stated, is a browser. When you open a folder in Bridge, you can see ALL of the files: text, jpg, raw, illustrator, etc. You can open all of the images from Bridge by double-clicking. Whatever application you assign (all have defaulted applications already set when you first open Bridge). And, as Erik said, all adjustments are done in Adobe Camera Raw and/or Photoshop. Where I use Bridge, almost daily, is for images I do not wish to, or need to keep. Two examples: I do a newsletter for my woodworking club and get images from members to add to the newsletter. These are viewed in Bridge and kept for archival purposes, but almost never seen again. In addition, if I take a photo of something I'm selling on Craigslist or on a Buy Nothing page, I use Bridge for that as well.

Before I continue, let me quickly point out that any application from Adobe that starts with "Lightroom" is Adobe Camera Raw with a Database. So, Lightroom Mobile, Lightroom Desktop, Lightroom Classic, and Lightroom Web are all based on Adobe Camera Raw.

Lightroom Desktop (icon is "Lr"). I have Lightroom Mobile on my phone, and when I take a photo with my phone, it will automatically show up in Lightroom Desktop (after transmission time). I love this functionality. For me, my big issue with LRD is that all images are stored in the Clouds, which is why my primary Lightroom application is Lightroom Classic.

With Lightroom Classic, all images are stored in attached storage drives. All of my images are stored on a 4 TB drive and is backed up to another 4 TB drive that is also backed up to the clouds. The former is in case of hard drive failure, and the latter in case the house burns down. I like sleeping at night.

Lightroom Classic is a true DAM (Digital Asset Management) system, where it knows where all your images are, and you can easily search for keywords and click selected keywords to find all your relevant photos. Now, Bridge also uses keywords, but I've found LRC's use is far more robust.

The one BIG BIG BIG thing you must always remember when using LRC is that you must do everything of image storage IN LRC. If you change the name of a folder or move a file in either Explorer or the Finder, LRC doesn't have a clue about that at all. If you make this mistake, when you look at the thumbnail in LRC, you will see an exclamation point (!) indicating that LRC doesn't know where this image is. You can right-click the file and let LRC know where it is, and all is well, but avoiding the problem is best.

Don't ask me how I know about this issue.

But what I do love about LRC is that I like to keep all of my images in subfolders. So, let's say I have folders of family parties I've gone to, and let's say I've got a dozen such separate folders. Let's also say that I need to find an image of Aunt Grezelda, who was at most of these parties. And, let's also say I've turned on facial recognition for all of the family and friends' faces. I can then go to the Keyword list, find Aunt Grezelda's name, click the "open" icon, and only images of Aunt Grezelda will be displayed.

Lastly, as I mentioned, I like using folders to store images. If I had your 100 folders, I'd import one into LRC, and then start sorting them into primary and secondary folders. Then import the 2nd, and continue creating new primary and secondary folders as needed, adding keywords (and facial recognition) as you go. You can change your mind at any time, but make changes only within LRC; never in Explorer or Finder. 

I hope this helps, but If that constraint is not to your liking, then by all means, use Bridge.

Before you begin, one thing to make clear in answer to your question, "Should I work through these images and folders before I import into Bridge?" You can't ever import anything into Bridge. Bridge is a browser and simply shows you the content of wherever you point it. It is not like Lightroom which has a catalogue to which to import images. So you can use Bridge to view, sort, move, copy, delete and rate your images. You can also add or edit some image metadata, but not all. Bridge does not have any image editing facility. You must open images in Photoshop or Camera Raw to perform edits. If you double click any image in Bridge, it will do this for you provided that you have preferences set appropriately.