I've done many of my old ones going back several decades. I don't know how many slides, but it was about three shoe boxes full.
I had a very good film scanner (Canon FS40000US) which will scan flat film or slides, but I had to get the computer set up with a new driver program. The original scanner interface has not been supported on the latest couple of operating systems. Once I got that going, then it was mostly a matter of time.
The resolution that you scan mostly depends on your intended use for the image files. If you intend to print, then you better get the resolution somewhere in the range of 300 dots per inch. If you intend to show them on a computer screen, then you can get by with less resolution. If you intend to edit and improve them in Photoshop, then get back to the higher resolution first. If you have some that might be serious gems, then also kick up the color depth at the scan. If you try to push the scan resolution much higher than 300 dpi, you won't have much to show for it except huge image file sizes and much more time spent. However, what you do for scanning depends a lot on the scanner that you select and the hardware interface that it uses to send data to the computer.
In general, a flatbed scanner is not what you want for slides. I admit to scanning a couple of slides with a flatbed scanner, but the results were generally poor as compared to a film/slide scanner.
Note that scanning time goes by the square of the resolution. In other words, if you see that a 100 dpi scan takes a minute, then the 200 dpi scan may take four minutes, and a 400 dpi scan may take sixteen minutes. With that in mind, a scanner with a super fast hardware interface may be worthwhile if you have a large number of slides. Which is more expensive, computer stuff or your time?
Additionally, by digitizing your slides this way, it will allow you to Photoshop-in some color corrections. I had many Ektachrome slides that were shot and processed in a third world country many years ago. Those had taken on an odd color shift. So, once you figure out the color correction for one, you can plug in the same correction to all of them. In some cases, the driver program will allow you to select what kind of slides (e.g. Ektachrome) they are, and it will plug in the color correction to all of the files for you.
Some slides will have minute particles of dust that you need to clean off. That works better than trying to let the scanner perform its magic anti-dust corrections. Some scanners will do an IR surface scan first to figure out where the particles are located, and then it will blur some of the scanned data after the fact to make it seem that the dust was eliminated. This works, but it requires a lot more time, and some of the sharpness may be lost.
When you save your result files, stop and think about what kind of media you want to use, DVD, CD-R, etc. I look back over time and see how many media types (e.g. Zipdrives) are now obsolete and unsupported by modern operating systems. If I had committed my slide scan files to those, I would be stuck. As a consequence, I keep my slide scan files in at least three physical places, typically as JPEG files on multiple hard disks (for easy access), plus at least one external storage device. If any of these start to go obsolete, I can transfer them all to some more modern thing. Be prepared to purchase some extra external hard disk drives, and those may be disengaged and locked up somewhere.
If you do jump into this, do not scan about a zillion slides and then go back to check on the result. You might get an ugly surprise about resolution, color depth, color shift, or something else. So, I recommend that you do a small number in the first batch, check them, then send them to a family member to have them check them. Then proceed to do all of the rest of the slides in the same manner.
–B.G.–