10 foot cables to external hard drives - how many? SATA extensions or networked drives?
My current setup is very similar - main differences being that I have a UPS and that I have a wireless keyboard and mouse combo. My desk, more of a table actually, is wood with a shelf underneath that holds the UPS, some plastic hanging file folders, and a few three-ring binders. And there is a rather flimsy back panel that does help hide cables running up to the monitor and speakers. Back panel to be replaced some rainy day and I will add holes, brackets, etc. to help with cable management. Does not appear that you would have that option.
I mark my cables on both ends - just colored electrical tape specific to one cable or another. Helps me, for example, identify which AC power cable or AC/DC adapter goes to what device. Main reason being that I do not want to accidently unplug the computer.
I keep the existing wires on the floor next to the floor molding but I run the wires through a 2 1/2 foot hollow plastic baluster used on decks, stairs, etc.. It was a scrap piece of baluster and at some time I will replace it with a longer piece. Coiling wires always seem to come undone and zip ties etc. just get in the way more often than not. Velcro straps are a better choice but seem to work or slip loose sooner or later.
Not a fan of coiled wires just hanging and self-supported.
You may have the option is to use a cable tray hung off of the back of the desk. I tried that for awhile but the tray forced the my desk/table away from the wall.
However, I am not certain about how that all may work especially if you regularly raise and lower the desk. You will probably need to rearrange all the cables with the desk fully extended to ensure that slack is available to freely permit raising and lowering the desk surface.
Another thing I do is put my desktop/tower up on a small wheeled platforms about 12" wide and 18" or so deep. One platform is DIY and the other was a salvaged commercial platform. Having the computers up off of the floor, even just a couple of inches, makes it much easier to move things around. If you have the leg room, just moving the desktop under the desk next to the speaker will likely make the cable management easier or otherwise help conceal some of the cables.
Main suggestion at this time: Google "computer cable management ideas" or similar words and phrases.
Narrow the search to images and just start looking for more ideas. Try out things that are easy, inexpensive, and can be modified, redone (aka "do-over"). If something works well, then you may want to try a more permanent or improved version.
Lastly, I sometimes think that those wires etc. all crawl around at night. What seemed neat and tidy one day all of a sudden becomes a worm nest the next day. Stay flexible - pun intended.