I'm working with the owner of a group of websites that are built on ASP/MS SQL. The sites are fairly old and have become unwieldy, difficult to maintain/update and costly to promote & market effectively.

The site owner is considering rebuilding his sites onto WordPress and I have floated the idea of taking this opportunity to consolidate the sites into one domain.

Our main hesitation is uncertainty that the rankings and other metrics of the original sites will be duly passed over to the new site. I'm familiar with the best practices of rebuilding a site with minimal disruption, but am less confident with the process of transferring content and pages over to a new domain entirely.

My questions are:
- Are there any ideal ways to structure the new site? My idea was to use sub domains for what are currently separate domains, i.e. from:

www.site1.com, www.site2.com, www.site3.com to:

www.site1.new-site.com, www.site2.new-site.com, www.site3.new-site.com

- Is it likely that 301 redirects will transfer old rankings to the new URLs? What kind of time frame are we looking at for potential disruption?

Any help and suggestions will be much appreciated.
Many thanks.