Well, you've given a list of the Scanner makes and models.... but what are the names of the OCR software programs that come bundled with them? Those are what you should be researching as well. Just look for one that allows proof reading if you want to correct any errors as you go.
i.e. Abbyy FineReader, OmniPage, and TextBridge OCR are examples of OCR software.
When you have your documents saved as Word text, your Office Word program should be capable of searching by date, word etc.