My estemed friends are correct,, you are off to a good start.
I would suggest you get the RENE guide,, and also get John Dougan's latest book on Rugers. That along with Ruger & his guns, by R.L. Wilson. Reading material is a MUST in collecting.
That said,, there are a lot of variations of the old models,, as noted,, over 200 variations of the Single-Six alone.
You might focus your collection in a direction based upon your budget, or allowable space in your safe. Example; Old Model Lightweight Single-Six's. Not a whole lot of variation,, but getting the BOXES & papers can take a bit of work. A good complete "display" of them,, with say the early catalogs & other paperwork with boxes, shippers, (even harder to find,) would be an easier goal than to try & get all of the OM variations.
If you wanted to expand a bit more,, try a section such as "Flatgates." A lot more variations,, & a lot more boxes, shippers etc to look for and it'll keep you frothing at the mouth when you get on the hunt for that one that's been elusive to your collection.
What I'm getting at is you can pick a specific model,, then look for possible variations within that model to focus on.
And you CAN do a display of a "group" that isn't complete,, and still have an excellent display. Usually,, when an example or two is "missing" we do not discount the display as we all know how hard some guns are to find. I recall one excellent display where radical rod built his dosplay,, AND included an "empty" spot for a missing variation. He included the info about that one gun,, but left an empty spot to fill. It was still a great display,, with a slightly different approach. And if I recall correctly,, he won an award for it.
My approach to collecting is a bit different,, in that I'm both a gatherer & a collector. I gather any & all Rugers that strike my fancy,, knowing that going after a complete set of anything is harder,, and I'd have to finance it by selling other guns. Since I HATE seller remorse,, I don't sell any,, but I buy Rugers as they appear. I now have several to where I could focus on certain theme's but still not enough to satisify myself in that I could do a good display. I also collect a lot of the old paperwork,, and THAT can be a bit more frustrating as a lot of that stuff got thrown away.
All in all, collecting is a great way to further your enjoyment of Rugers,, as not only will you find collectable guns,, you can find some "shooters" of the same guns to enjoy!
You are on the right track,, so get the books & start reading!