SEO Issues: Canonicalisation, Session IDs + Ecommerce

Some SEO issues to be resolved:
1. Canonicalisation
There is a mix of non-www pages and www pages. I want it set up so that all non-www pages redirect to the www pages.

2. Session IDs
I have a duplicate content issue in that when on the site, urls with "pmsession" in them are showing and are getting indexed. The content on the urls is not changing so I don't know why there are session ids. There is no login on the site.

3. Image ALT text to be added to the images on the site. Approx. 50 images on the site.

Also, if possible:
4. Creation of 18 product pages. There is a CMS to assist with this. It will be a copy and paste of content from a site in another country that supplies same products to us. Paypal buttons to be added.