Looking at the solutions shown in the thread printed above is definitely a good idea.
The scanning gear as per Valoi or a Nikon ES-2 provides the best possible solution and stability for single size scanning. These solutions can be transformed into a vertical setup, so that one can work more easily with film ends resting flat on a table (or something suitable).
Vertical setups can also serve to copy prints - if the lens and camera can be moved or fixed at different heights.
Alignment is easily done with a mirror, and Vlad’s test target provides extra info if you need it. A geared head is certainly quite comfortable, but shims can do, if applied carefully. I use a thin paper-like tape that does not flow under pressure. I’ve recently acquired a Leofoto G20 geared head. It can carry 20 kilos, not that my gear is that heavy, but it pays to have some overhead to prevent wobbly setups. I’ll test it on my latest contraption in the near future.
Focusing…by AF is not good enough. As is focus peeking. Manually focusing with enlarged live view is what helps to get the best possible focus, even with lenses that have focus shift, provided one can use live view with closed aperture.
Vertical vs. Horizontal: Most gear is meant to be used in what translates to be a horizontal setup. Using gear in a vertical setup could stress portions of the gear in ways that were not part of the design process. Therefore, getting heavy duty items will benefit the rig by less wobble and/or slack. This is why I used gear from video rigs like e.g. an ARRI style baseplate. Video gear is often more expensive, but I found that e.g. Sirui and Proaim provide sets of gear at reasonable prices. Note that a full cage for the camera increases stability.
PS Note that I’m not paid for listing anything here.