Prescan the original and decide on the final cropping. Scan the image. Resample the image to the final resolution decided at 1. Apply Unsharp mask to the image. If the intention is to scan photographic images only then a 36bit A4 flatbed scanner with a Dmax of 3.0 or more and an optical resolution of 600ppi or more is sufficient.
Transparency is a different kettle of fish altogether.
These dedicated 35mm scanners will have a resolution of 2500ppi or better with a minimum Dmax of 3.2. Although the prices are coming down these scanners are quite expensive. These will accommodate 40 high quality or 100 standard quality images per CD and usually cost around Lm5. As far as I know, this service is not available locally. If one intends to scan X-rays then an A3 flatbed with a transparency hood is ideal.