Keep forever.  Regret is not having them the day after you toss them.

Go to a big box store like BestBuy and order a scanner-fax-printer-copier.  They are under a couple hundred bucks now and have autofeed trays to stick papers in and automatically scan and convert to pdf.

The best one is the wireless units that operate across an office over remote, wi-fi and accessed by any number of computers with no cables needed. 

Plan to scan one box a week and at the end of a year you'll have 52 less boxes;  not bad, eh?  This means savings in storage space, plus no outlay for somebody else to do what you can do with a bit of forethough and planning:  Good business there for sure!