Wow.....this is exciting!
I know how nervous you must feel, this being your first and an unexpected pregnancy & whelping. But do stay calm, for your sake and for your mama. Chances are probably good that everything will go smoothly come birthing time. You just want to be sure you don't let her out of your site until after she has her pups. The bath you asked about could wait until after the whelp. Things may get pretty messy then, but the mom usually cleans herself and the pups up pretty well; with a little help from you as well.
Good luck to you....use the numbers you were given and come here for help when you can during whelping. There will be plenty of us here to help however we can; even if it's just for moral support.....I know I'll be watching for the good news!
Oh and I highly reccomend the xray. It gives you a good idea on the number of pups to expect and their size in comparison to an easy delivery.