Long runs and USB3 don't play well together. Have not used USB3 with active extenders but would still be hesitant to use just because so limited with straight cable. I've used 50ft usb2 with active extender bu was not doing anything that taxed the setup.
As far as the PC at scope....
A question or 2 about your setup.... is it permanent or do you have to setup each time?
I ask because I have to setup (roll the whole setup out of the garage, plug in network and power). I had a mini-pc setup and used TightVNC to remote from my laptop. Initially I was using wifi but performance was sporadic so I put a network drop in my garage and then ran a cat5 to the mini-pc. That worked but I still found myself taking the laptop out to the scope with me to do the alignments, selecting guide star etc because I needed to see the screen. Trying to use the on-screen controller for alignment just didn't work well.. But the laptop was still on wifi (sporadic) so had put in a hub at the scope to plug into when I went out there .
Finally came to the resolution that this just wasn't working well.
So, I'd already bought a new higher powered laptop for image processing so decided to take out the mini-pc and just use my old laptop at the scope. Now, I use the old laptop at the scope (on cat5) to get setup and acquire images. Once setup, I close the lid, and go back inside and use my new laptop with TightVNC remote to run everything.
For me, the mini-pc via remote just was a pain. Once all is set up, it was fine...but getting there each time was a pain. If a more permanent setup, it would probably be fine. So now I use the old laptop at the scope for setup, focus, and selecting guidestar. I start guiding and acquisition then go remote from there.