I'm using RSD with the blank Foundation template. What width should I start with when building a new website? Some say 960 pixels. Other say 980 pixels. I will be scanning numerous photos and need to know how many pixels wide to make them.

Why Limit Yourself,,RSD works from designing web-sites from Mobile Up to Desktop. Start from the lowest break point

A rule of thumb for images for mobile is not too large as it takes up a lot of bandwidth and can make for slow loading,
For larger screens & PC's thats not too big a problem

The great thing about RSD is that you can change the images as your width gets wider.

So say from about 300px to 640px wide,, you can make your smaller images around 450px wide
then from 640 upwards you can replace the image with a larger width say around 900px this will take you to 1024 px size , after that the sky is the limit it then becomes up to you as to how wide you want your web-site to be,
when viewed on larger monitors, so if you decide you want to make the web-site say 2000 px wide then your i mage needs to be close to that

get one or two images ready at different sizes and starting at the bottom (just left of the lowest breakpoint insert an image set the width of that image to what you want and see how it looks,, move up to the next breakpoint, and insert a larger size image etc etc

I have a video which goes into all of that, but I am updating my web-site at the moment i can put it up again if you can wait as it won't be ready until tomorrow (Bali Time)

Good luch

Wayan