I'm not familiar with Alchemy - but from your example above it should be fairly straightforward.

It looks like your example shows that 12345 is a unique ID that is also the document. 

If that's the case I'd work on getting all the metadata transferred into a database that workflow can access (if it isn't already). If the alchemy items are always single files this should be rather straightforward from here - just import those files using import agent, then use workflow to take the name and search the database for the matching ID column. Take the metadata associated with it in that db table(s) and copy it to the new fields in LAserfiche. 

If there is NOT a windows like file structure in Alchemy (or other migrated systems) then in my experience I've found it's useful to copy everything into new fields called migrate_fieldname1, migrate_fieldname2, etc in one giant template.

Then later you can run different workflows to file it away in whatever new template & filing structure that you want to use. That way if your client doesn't like the structure you can move it again. We've moved many customers from a search based product called Kwiktag over to Laserfiche and sometimes I've found migrated customers take a while to get used to using windows-like file structures after they've been used to a pure search system with no filing structure. What they want after two-three weeks of use is not always the structure they wanted when designing!

Luckily Laserfiche makes it easy to refile/resort as long as you keep all of that metadata!

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