I reviewed the requirements of the original poster, and subsequent posts, and determined the following.
1. The OP has a wide variety of formats and media, ranging in size from 4X5 to small format, and some color.
2. The final goal of the OP is to make amazing large scale prints on the order 6’ x 8’, very roughly speaking.
3. The OP already owns a good camera (a7r iii) for digitizing.
Based on my own experience in scanning, which goes back more than two decades and includes use of Epson flat bed, professional high end flatbeds such as Eversmart, drum scanning, and digitizing film with an a7r ii and iv I would recommend the following.
1. Since OP already owns a good camera the least expensive and most straight forward solution to high quality digitizing of the film is to buy a good macro lens and use the camera with a copy stand and led light box.
2. To get the most from the 4X5 slides the OP will need to make at least 4-6 shots and stitch the results, and perhaps two shots with stitching with the medium format film. The a7r iii has pixel shifting but the end file size is still only 42 mp, not the 240 mp possible with the newer Sony a7r iv, or 150 mp with the Panasonic. However, having copied film with the a7r iv my opinion is that 4-6 shots with the a7r iii will give better results than pixel shifting, if getting as much information as possible from the original film is important, as it probably is if 6' X 8' prints are needed.
3. For highest resolution the OP will need to use the macro lens at an aperture of f/4 - f/8. Beyond f/8 there will be diffraction which may reduce resolution below sensor potential, below f/4 plan of focus is highly critical.
4. Using the lens at f/4 or less will require very precise focus, with slide or negative fluid mounted on glass, or stretched flat on AN glass. Emulsion should face the lens.
The a7r iii of the OP is not very heavy so one probably can get by with a fairly duty light copy stand if budget is an important consideration.
Sandy
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