If I was going to use a laptop as my main computer with all my farm records I would want a  solid state hard drive in it and would want everything backed up to the cloud or an external hard drive whenever it was docked. This would help with lost data when your laptop gets lost, stolen, or broken.
Instead of a  laptop you might want to consider a to Surface Pro 3 Tablet.  Much easier to carry and the 12" screen is big enough to see.  Only drawback is the dollars for the complete system.  Could step down to the Surface with a 10.8" screen and atom processor for about half the dollar amount.

If you like the idea of a Surface table, but  not the price, then Microsoft sells refurbished on ebay with a keyboard for $849.  The  Surface 4 is expected out in the next month, so these may drop in price more.