I agree wholeheartedly to the two external drive solution. The advantage to committing to using Lightroom is the availability of keywords. This feature, faithfully maintained, makes your choice of file structure essentially irrelevant. What does become relevant is your choice of keyword strategy which can be as idiosyncratic as you like. Just so long as you can be consistent about their application to your images, finding an image from a couple of years ago will be no less easy than finding one from yesterday.