Things definitely tight with the tall sump under the stand. Fitting & maintaining skimmer down there will be a nasty chore. In fact, working on anything down there will be a hassle. Might consider something a little shorter.
Sumps are great & I'd love to have one myself, but I've been running without for years. Not saying you should, but the reason I mention this is that because I don't have a sump, my skimmer is external, mounted on a little stand next to the display. It's a diy wooden air diffuser skimmer that came with the tank when I purchased it years ago. I realize you've already purchased a skimmer but figured you may want some additional info, perhaps for the future.
There has been much discussion, some research & plenty of new developments regarding skimmer technology over the years, but the bottom line is, most of them end up being roughly equal in performance. Even my old tech air diffuser rig does a fine job of pulling organics out of the water. The main factors determining skimmer efficiency (aside from physical size) are bubble size (smaller=better) & contact time between the water passing thru skimmer & bubbles (longer contact time=better). Wooden air diffusers need to be changed out periodically, but they produce some of the finest bubbles I've seen. A small power head in a skimming box in my display moves water slowly through my skimmer. I can regulate the height of the water column by either throttling the power head, the air pump output or adjusting a valve on the skimmer return line. Low power consumption & quiet operation are a couple of other pros to using this old school method. Cons are that the thing is sitting there next to my display & I wish it was a little taller to lengthen contact time.
Here are some photos, a few years old, but should give you an idea of how an air driven skimmer works
A search on air driven, counter current skimmers should bring up plenty of additional info for your reading pleasure. Some day I will have a basement sump which will feature a 6 foot air driven skimmer!