Jan:
Scanning - using a film-scanner and not a flatbed - is a great way to bring slides into the digital age.
I wouldn't put images with any micro-agency though. Your images will end up selling (all rights in perpetuity meaning that the buyer can use the image sold for whatever they want for how long they want with no further payments to you. Instead I'd recommend signing up with an agency like Alamy or FotoBlibra. The licensing fees are much, much higher than the micro-agencies. This is especially true if you can provide something that isn't readily available through the micro-agencies.
Mike Karlsson
PhotoSource International
www.photosource.com
mike@photosource.com