I have an old Epson Perfection 2400 Photo scanner which scans 35 mm slides at 2400 pixels per inch. The result is very good by my standards. Of course it scans full-size reflective pages as well.
Here's a sample of a slide I scanned, note the dust in the sky.
http://members.toast.net/rcarpen/silverton1970.jpg
A friend has an Epson Perfection V500 scanner, which is a modern replacement for my model. It seems to work at least as well as my older unit. The newer unit offers "dust removal" which mine doesn't have. You can turn off this feature if it causes you problems.
These do NOT come with the horrible software "baggage" like HPs do. Just nice Twain drivers with straightforward control panels.
The V500 is in the region of $150 on Amazon in the USA.
I'd certainly go with an Epson flatbed with slide attachment in the future.
When you scan positives (slides), dust shows up as black dots, which aren't terribly offensive to me. When scanning negatives, dust shows up as very white dots - far more offensive. I haven't investigated whether the Epson anti-dust feature helps with dust on negatives.
seacue
Edited to correct price.
Further edited to state that these meet your criterion #2 (select from preview before scan).