Something else that is sometimes forgotten - LDV's notebooks were for his personal use; none (that I recall) were ever published during his lifetime, and then they were "lost" (squirreled away by others would be a better term - ie, "lost" as in "stuffed in an attic in the back corner and forgotten about until passed - yet again - after the owner died") for a long period before being rediscovered and finally published much later - more for curiosity sake than for any knowledge contained in them, as most of it was out of date and/or rediscovered by then.
I doubt that he would have cared, either; his interest in bettering his knowledge and more were for his own sake and nobody else's. Many of the things he noted down and learned, then expanded upon, were actually well-known concepts and such that just hadn't been "written down", or if they had, they were generally done in a far inferior fashion.
Ultimately, though, they were for his own study, and maybe for the few others he (possibly) showed them to (students and/or people he asked questions of would be my guess) - to convey ideas very clearly, as if the actual device or object in question were in front of him or another. Most of the prior attempts at conveying such information could be termed more as "schematic" than as representative of actual form. Some weren't even that clear.
As others have noted, I wouldn't bother with trying to become an expert in everything today - that's a near impossibility. Rather, focus on bettering your knowledge about a wide variety of subjects that interest you. Learn how to apply knowledge from one area to solve problems in another domain. Learn how to integrate knowledge across domains to also solve problems, or come up with creative solutions or further ideas in another domain. In short, treat learning and creativity more like a child; play with it, and enjoy it.
That's a large part of what it means to be a "Renaissance Man"; to me, it doesn't have anything to do with being an expert in any number of particular fields, or even one field. Rather, to me it means having a broad knowledge base, and finding joy in applying that to learn in other areas and solving problems new to me using that - and, when I can or when asked - passing on what I have learned.