Hi Johnas

In our view add it to the main site.  If you go for a split solution you dilute all the great work done from both sites.  Adding a shopping section to the site will add more traffic to the XXX.com site and therefore will also bring in product specific links and recommendations.

There are some very learned colleagues here on Moz, who will be able to offer more thoughts about your thinking.

As always with SEO, distill the essence of your company and present it in a unique way.  Unique in respect of making sure all reading material is written with your own words, with a moderate sprinkling of keywords.

Adding your ecommerce to the site enhances and leads the reader from reader to buyer

Hope that this helps

Bruce

You can have as many 301s as required, no problem at all.  Google will not mind at all.

You will lose some authority of between 1 to 10% via the redirected to...pages, but this is to be expected.  DA reflects the site and PA the page, so if you need to change the domain, then you will drop a bit, but will with good SEO bring this back up reasonable quickly.

WMT only specifies which version of the site you prefer, so Google knows that www.example.com and example.com are the same site. if you don't make a specification Google will not make the association and will class both as separate domains.

Bruce

Without know what kind of site you have it is hard to gauge.

Ecommerce Keyword ranking swing wildy as these are often used in conjuction with Adwords and bidding. So whilst you might have a great keyword, if this is a seasonal or on trend product then the competition changes dramatically.

If you have a blog or a company site, not in ecommerce, check what is happening in the industry and see if your keyword has gone on trend.  For example: Blue LED.  a few days ago this was not the hotest topic around, but since the Noble Prize has just been awarded, this phrase will be more volatile, but will drop back once the excitement drops.

So in essence for the above, if you keyword was rankng well, it might be that you where in a niche area and ranked well even with other SEO issues present.  Once competition hots up, others might well outrank you.

If you can give us some more info about your site, that would be a great starting point

Bruce

It is a really tough one to deal with, although Google does recognise ecommerce data for products and recognises that duplication of product titles and descriptions happen and does not from what I understand have a major issue, although you will be competing with the others for the key word and phrasematches with your own site. (edit expand explaination)

Depending how your own site is structured, product popularity etc will give an indication of how well you will rank for your own site versus the big boys.

My view is that whilst you should use your own site to reflect your brand identity, expand the Brand / Category pages with fresh new text to add authority to your site, and look at all the channels collectively and do not worry if your own site is appears to underperform compared to the rest.  This is normal as the volumes of traffic and exposure will drive sales.

Hope that is useful

Bruce

h1 tags are useful, but are not needed by Google, as they will crawl the page to see the content.  However if you have h2 h3 etc tags, but don't have an h1 then crawls will not read any tag at all, as they must be present, completed and sequential.

Hope that helps

Bruce