Re:
Dynamic range is being able to pick up both the highlights & lowlights.
As a slide is a different chemical makeup to a negative it tends to record a greater dynamic range - and hence the spectral range and appearance of a slide is 'brighter'. You lose this often when scanning from slides, including printing onto paper from a slide, even in a photo lab without a lot of manipulation. 14-bit is a good place to start. Don't worry too much about high dpi; range is more important.
What the greater dynamic range does is allows the scanner to pick up the higher and lower light ranges - just like a greater dynamic range on a TV, or a greater frequency range on an amplifier, headphones etc; you just get 'more' of the image in.
The Nikons are good scanners, pretty straightforward to use, and if you can find one, AGFA Duoscan (Not AFS!) scanners can be are very good as well. Best photolab I used was a Fuji, and the scanners were superb, but I never used one of their compact/desktop scanners, they did seem very well-made however from those we stocked BITD.
One issue potentially though, is software support, in that many of the scanners were XP-compatible but required drivers to be installed from disc when first brought out, a lot of these manufacturers no longer provide support, manuals or drivers online however, and if you have later Windows...no idea.
You might of course be lucky & find a Leica..