as long as you don't change your URL your ranking should not be affected. But you would want to contact Google and get the best answer to your question. Even SEO companies would give you a variety of answers. Best regards!
Benik Hovsepian, M.B.A.
Top ranking in Google, Yahoo, Bing & MSN Worldwide
Real Estate Services Since 1988
Having an additional website or blog will only help your business. Find out what works on your current site and add it to your new site with links going back and forth. The whole premise with viral marketing is to link one by one then two by two etc...
I have 10 active websites that piggy back each other own specific marketing maximizing every dollar spent.
It only took a couple of weeks for the switch to totally be reflected on Google.
Assuming everything still works correctly, then start adding your new content. It will take Google a few days to spider (or find) and index your content. You might also want to check out some references on SEO writing; this will help you to write your content in a way that will make it easier to index (and will have the added bonus of making your content easier to reference--which will eventually help to increase your pagerank).
I would copy and paste the same content and duplicate your links. If you have identical content and only move to a different host, you should be ok and not penalized.
If you add a blog, that is fresh content, which Google favors. It should get indexed/crawled quickly and have a positive impact on your search if you keep up with blog entries each week. With a blog, you will have more flexibilty with making sure your key words/phrases reflect how your buyers and sellers will search in your area.
Hope this helps.
I have asked this question several times and have had several different answers given but the consensus is yes it will affect your ranking because the actual content is changing. That is one reason I have not changed my website as well. Hope this helps.