Jumping in, lots of photos to import

If the images are already located where you want them to be then you might as well go ahead and import them into the Lightroom catalog. That isn't going to move the images anywhere, the process will just add them to the catalog, which is a database, and enable you to start editing them or deleting the ones that you want to get rid of. If you still want to move the images around and organize them more to your liking, it might be better if you did that before you start importing. This is especially true, in my opinion, since you are new Lightroom. Some new users seem to have difficulty understanding the relationship between the catalog and the actual images.

A few things first: I am assuming that you are using Lightroom Classic and not what Adobe now simply calls Lightroom whihc extremely confusingly is a completely different program that stores all your images in the cloud. Your volume of images is not reaslly conducive to cloud storage so you are probably talking about Classic. If that is not the case do not read further.

Second: Were these images in Lightroom Classic before? If so, you should try to recover the catalog files and build from there. If not, finally some answers. First, do not worry about the current folder structure on disk too much. There are two ways to approach this. One is to import everything in place using the add mode in Classic. You can then use keywording and collections to internally organize the images while keeping them all in the same place on your drobos. 

A second approach is to set up Lightroom to import into folders organized by date and use copy or move while importing. This will automatically organize all your images by year, month, and date on your hard drive. After that, you would do the exact same thing by keywording and making collections and smart collections as before. 

The important thing to realize is that it really doesn't matter much where on your drives the images are located. You can organize in collections and collection sets, keyword, etc to your heart's content while keeping all the images in the same location. You can easily find images by filters (can be by date, camera used, lens used, etc.) and searches and smart collections. The only thing to remember is that you shouldn't move around the images outside of Lightroom Classic as Classic will lose track of where they are.