I'll throw out a few ideas:
I think two external HD's for travel are excessive, assuming you do what Michael taught us: don't reuse your cards while on a trip. Have enough cards for your entire trip. All the cameras I have now use SD cards. This makes it easy for me to have a couple of nice plastic holders with my cards, and I can always keep the cards on my person. So between my drive (whether internal/external) and my cards, I do have two full sets. You could have 5 external drives, but they will likely all be together, and if they get ripped off, you are done.
I have mostly given up editing/deleting while on the road. Even if you have a killer laptop screen, you don't have the resolution of your large home monitor, right? I prefer to wait until I'm home and review my images on the best equipment I have.
2.5" laptop SSD's make awesome external drives. Many come with USB connectors so that people can clone their existing drive before replacing with the new SSD. Well, just use it as an external drive instead! The size of a deck of cards, half as thick, and you can get 256gb for about $170.
I am a pretty active photographer, my LR catalog has 140k images. (I actually have two other catalogs, seldom used, with another 25k, kid sports, some other projects). The catalog, previews, all my images, some other stuff, takes 2.2gb. I now use usb3 drive docks with regular internal drives poked into them. (I call them toasters). Drive capacities have kept up with my usage, there's no reason for me to have them on multiple drives. I'm now using a 4tb drive for another application and it works fine. With two of these "toaster" drive docks I can easily back up to other bare drives. With a bare drive, you can plug it into nearly any computer, you don't have to worry about losing a powersupply or whatever. (I'm PC btw, I know things are different in Mac Land.)
By using the drive dock, I can plug this drive into ANY pc type computer that has LR, and get to all my images, my entire catalog. It's super flexible, way better than having all the files on an internal drive (IMHO). With USB 3, there is hardly any speed penalty.