Don't get too caught up in the "Blue Coolaid" virus that can infest your wallet big time ...and lots of times unnecessarily. All that "stuff" is very convenient when needed but most of the time inter-changing a few things works just as well but a lot cheaper. Don't get me wrong ...I fell in with both feet when I started the Dillon trail but in hindsight I could have saves many dollars for components if I had just slowed down and thought a bit.
As G-man says "the tool heads with each caliber die and it's own powder measure" is nice, he is very right about the tool heads, but a bunch of powder measures surely is not a necessity...powder bars are a fraction of the price and once set can be left set and changed at will in a few seconds.
I have a case feeder for the one 650 I have left and have only ever used the large pistol feed plate in it (my feeder came with a Small & large pistol & a rifle plate). So far I have used it for 9 mm, .38 sp, .45 auto, 45 LC , .223 and 45-70... all with the same plate so I don't know if the others work "better" because I have never had a hick-up with just the large pistol.
Another thing to pay attension to that can save a few bucks is the "conversion Kits". Quite often parts can be used for different calibers without buying a totally different "kit". Two shell plated will load most rifle calibers, all you need is a different set of locating pins or maybe a feed funnel for a couple bucks. The back of your manual should have a chart to order separate pieces, just compare the parts # of the calibers you want to the ones you have.
Another thing to know about your 650...it can be used very efficiently as a "single stage" press by just disabling the advancing mechanism and using which-ever station you need for a "batch" load session. To disable either remove the two socket head screws that hold the advancing lug to the frame(my recommendation) or remove the long spring from underneath the ram head (this spring can be a bugger to get hooked again).
