Yo! Brahman here! Looks like this is a topic I can contribute something to!
1.) IMHO: Forget photographing! OK - it *is* the fastest method, BUT you will also photograph all the scratches, dust, faded color etc. and have no really good way of removing it.
2.) You need a scanner than has a separate INFRARED lens, that can do a separate infrared scan to catch the dust and scratches. Why? Because a slide is tiny. You don`t look at it in this tiny form, though, you blow it up! And when you do this, like in "Honey I Blew Up the Kid" any dust spec will grow to monster spec.
The infrared scan will detect the specs and scratches, and tell the software where to fix the scratch. Therefore, they will get fixed only at the spot where they occur. You can do this manually, but believe me, you only want to do this if you work for Vogue.
I have attached two videos showing this method (using an older version of Vuescan, the more recent ones have even improved the dust removal process). The video with the long title you may want to watch several times to really see the big problem specs that are removed, because the slide is very busy.
Yes, there is some software that will try to do post processing and try to detect the specs and scratches without infrared, but it is
a.) unreliable (no infrared markers to use)
b.) will overdo the fixing and over soften (like in washed out detail soften) the entire image.
You can either buy a dedicated slide scanner (for dedicated I would recommend the later Plustek models) or any Epson and Canon flatbed scanner which has this dedicated infrared lens. The more recent ones have an LED lamp and need no warm up time.
If you buy a dedicated one you will usually get better picture quality, but I (as opposed to many other people) do not favor buying a used dedicated slide scanner, because they have more sensitive mechanical parts than flatbed scanner and you cannot know what condition these mechanical parts are in and when the scanner will fail.
I have just recently sold my recent Canon 9000F flatbed for really good money and bought an old 5200F flatbed for very, very little money (~20$) and am still very happy with its speed and slide quality. Very sufficient for holiday snapshots, but of course not for high quality arthouse photos.
3.) The better the software, the better the end result and the less time you will need. At hamrick.com you can buy Vuescan Professional, which lets you save RAW scans.
Certainly, this is the best way to start out: Make 64bit RGBI (=Red, Green, Blue, Infrared) RAW scans, which INCLUDE the infrared channel (saving it in the file, so there is no actual dust removal *processing* while you scan). Just feed the slides into the scanner and make assembly line scans while watching TV etc.
This is the fastest way to scan since almost no processing is happening (which slows down the scan due to additional CPU time) and one can do all the processing later (every single slide, or all of them as a batch).
When I started my slides, I did not do RAW scans with the result, that I needed to rescan ALL my slides again after I learned how to process them well (this can be a steep learning curve). BTW Vuescan will also freshen up the faded colors so that you will think the 40 year old photo was shot just recently.
My Canon 5200F has 2400x4800 resolution and I scan with 2400 for slides. My Canon 9000F had 9600x9600 resolution and I scanned with 4800 for color slides. Believe me, the results were not very different. The explanation for this is very technical and would definitely be outside the scope of this post. Any good Epson or Canon flatbed with infrared will probably do, though I would stay away from the really old ones, since scan technology has improved a lot in this millennium.
Another tip: *Sort* the slides beforehand in a quick visual process using an old projector or viewer. Most of them are probably not worth keeping. Select the good ones in a fast selection process, and only scan those.
Also, consider using a scan service, they will usually do a decent job (if they use Vuescan - most do - you could ask them for RAW scan files including the infrared channel, so that you can process them yourself with Vuescan per your gusto later). But find out if they ship to India or China or really scan them locally, just so that you can assess the risk of losing the slides in the mail.
That is my 2 cent worth of advice in a very compressed form.