If I am looking to clean up my database can I do a mass search for duplicates? save the file and at a later date work on merging?
Yes - go to Contacts menu » Find and Merge Duplicate Contacts. There is dedupe documentation available.
The tricky question is, "What represents a duplicate contact?". For some organizations, two contacts with the same record might be a duplicate; for others, that's not enough to determine if it's a duplicate.
So while the Using rules and merging duplicate contacts manually section of the documentation might be all you need (e.g. if you can use the built-in "match on emails only" rule), you may need to read the rest to tell CiviCRM what constitutes a duplicate for your organization.
There is also the Extended Contact Matcher extension which could be used to match duplicates. This extension is more enhanced than the default dedupe functionality.