A developed site I have my eye on went expired with the registrar about a month-and-a-half ago. The domain was in use over ten years.
If the owner does not intend on keeping it, I would be happy to carry on with it. But:

a) I'm wondering how much time could be left to get the domain back up and running without significant damage occurring to its current reputation with the search engines. - Can't seem to recall specifically at what point in time domains become available to other consumers.... but I do recall that domain name holders have at least some right to call the name back to themselves within a given period.

b) I would like to have the prior owners blessing, however can't seem to get in contact with him or her since privacy was chosen on the name. Believe the link has been severed to the actual nameholder ever since the name became no longer active.

I see no reason in using the prior sites, basic page tags - but would not re-use the actual content again of course. Isn't this generally an acceptable practice? Is using all of the sites page tags "a duplication of structure" and can this only be done in moderation or by full force, as long as no duplication of content occurs?