Dr_Ju_ju

you may have a dodgy, mount to handset cable. If you have a spare ethernet cable to hand you could try try that instead (yes they will work as they effectively, are just one to one cables) From your picture above, it appears that you are using your mount solely for imaging ?? if so, then I'd suggest that you forget the handset and drive the mount directly from the PC via a USB to serial connection ...

What mount is it ?? For computer control, It's usually better to forget the handset, and drive the mount directly, using either a USB to USB lead (newer models), or a USB to serial adapter.

Is your power supply good & accurate (12-13volts)? If you power up the mount, without the handset connected, does it keep slewing around ?? Trying ascertain whether the problem is with mount or handset ..... If its with the mount, and depending how old it is, you need to either contact the retailer and\or undo the control 'face-plate' and check that there are no obvious signs of damage on the control board. If the problem appears to be with the handset, firstly, try re-flashing the firmware.

1st off, does "device manger" manger recognise that something had been plugged in ?? if so you will probably need to install some drivers for the PC to properly recognise the mount.... Also I suspect, as the WiFi is active, that it will need to be disabled before the USB port becomes active ??

If you're not going to change the EQ3-2 mount \ EQ5 tripod, albeit with a GOTO retrofit for the EQ3-2, then apart from easier\computer control, then I don't think much will change.... If you were to stretch your budget to a used HEQ5\EQ6 then it would be different matter....

I don't have or know your mount, but why do think its the motor at fault ?? Do you get the same result, if you remove the drive cable, from the control box ? and\or the motor itself ? have you tried swapping the RA & DEC motors ? are all the cables ok ? .....

I don't have one, but I have had similar issues with older gear while plugging it into a USB 3 port. If I plugged it into a USB 2 port, it usually worked ok, worth a try, if you can ??

With such large files, I wouldn't store them locally on the controlling computer, but to some form of network storage device, but then, to ensure reliable data transfer, I'd forget about using WiFi, and instead use wired Gb (multi) ethernet.

As well as the cost of the camera, you'll also probably also need to spend the same on computer with guaranteed USB 3.1 \ bus spec hardware.....

I have 2 600D's, one modded & one for general used, I find them great & easy to drive, especially with adding Magic Lantern, to expose additional control... & below is a single image taken earlier this year....

I don't know the camera (I use Canon's) but driving the camera using O'Telescope's Backyard Nikon (https://www.otelescope.com/store/product/11-backyardnikon-20-trial-edition-otl-byn-t/), should allow setting time for the mirror lock.

You can do the scaling in PrusaSlicer, which I've found to be accurate.

Depending on what colour\backing etc. I found these to be reasonably priced https://elpanelandtape.co.uk/el-panel/ or these https://elwirecraft.co.uk/product/white-el-panel-in-many-sizes-a6-a5-a4-a3-a2-and-a1-2/

The basic design can be done in a number of websites\applications etc. and depending how 'good' you want the part to be, e.g. Tinkercad (https://www.tinkercad.com/), OpenScad, you may even find what you're after on Thigiverse (https://www.thingiverse.com/). Once you have the design model (usually either an OBJ or STL file) you then need to prepare the the model for printing. This usually entails 'slicing' the obj\stl file into thin layers for the printer to 'print'. These days I usually just use the free PrusaSlicer (https://help.prusa3d.com/en/category/prusaslicer_204), but I also have paid for software (Simplify3D). As for getting the resultant 'sliced' file printed, what you are proposing at 273mm external diameter, would be too big for most of the 'home' printers, although I have one capable of 300mm diameter, but you could alter the design to split the model into multiple sections, to make it easier to print. As for printing shops, I'm not sure what is available at a reasonable cost ??

Have a look at Robert Brown's Arduino Focuser Pro2 (https://sourceforge.net/projects/arduinoascomfocuserpro2diy/) I've built a few, and with the software\drivers that Robert had written, means they can work with all the main software systems Windows\Linux etc....

I take it you're running on Windows, but other systems could also do it as well, you can create a small batch file that will delete the files, that can then be run by the "Task Scheduler" system at pre determined times e.g. every 15 mins

does the software 'calling' the Ascom driver have logging enabled ??

As you have the Pi (not sure if its powerful enough, due to its age, but as it also doesn't have a USB3 port....), but the simplest solution would be to install Indi\Kstars etc. onto it, have a look at Home (indilib.org)

As I use BackyardEOS to control my DSLR, I save all the images to either the local computer, or directly to a network storage location....

If you use the external desiccant tube, then you can't use the front 'solid', so to avoid the fan outlet grills, you are forced to use the rear parts which make for a very front heavy mounting, unless you design something that can also have some front support...

A variation on the above, especially if you have\access to a 3D printer, its relatively easy to knock up something that can hold a pair of M4 bolts (I think that's the size, but may be M3) to do the job...

From experience I'd forget the 10M active cable, as I've never found them any good..... IF your set-up is permanent, then I'd consider sighting a small single board computer (Raspberry Pi3\4, Pine64 Pro's etc...) at the scope and then controlling everything inside... If everything is running on the SBC, then interruptions due to bad connectivity won't matter so much.

All my Win systems have been 64 bit for years, and as long you have the appropriate 64 bit drivers, for those bits of kit that require them, then you should be fine... Bare in mind that you can still run 32 bit code, and most of the applications that you want to run, will still be 32 bit, its usually specialist, targeted apps that make full use of a 64 bit platform.

sounds like the ubiquitous problem with USB leads....

I also run the USB2 version in conjunction with the 1600, using the 1600's hub with filter wheel & never had a problem, but the all other connected devices are connected through dedicated USB hubs either 2 or 3... If you're brave\confident enough, it may also be worth checking how much throughput you're actually getting on the USB ports, following this (How can I view USB device bandwidth allocation in Windows 10 - Microsoft Community) will at least show you what your getting & whether there are any bottlenecks...