how long is a pregnancy with dogs & when should you notice first signs?

Approx 63 days. You may not notice any changes for the first five weeks. Look out for changes in nipples (pinker, more pronounced), frothy vomiting early on, slight change in behaviour (more 'precious'). Can be very difficult to be sure. Scanning is possible from about 30 days I believe.
Lorna

The vulva may stay slightly larger than normal at the end of bitches season. What breed is she?

You could go the library for some books.

Although 63 days is the "guide line" for full term, bitches can whelp from 58 days onwards, so you should have everything prepared by day 56 at the latest. If she is going to whelp somewhere different from where she sually sleeps you will need to get her used to her new quarters as least a week beforehand.