I've also pitched the uniflow powder drop and use the Lee Auto Disc powder thru the expander die. That makes the Pro 2000 like a 6 stage press. I have the sizer die first, then the powder/expander, then a check die, then a seater, then a taper crimp die.
As GW Staar mentioned, the RCBS Powder Expanders work really well with the Uniflow to allow you to expand and powder-charge in one station. I now have all my dies set up this way: I purchased several Hornady lower powder die assemblies (very similar, almost identical, in fact) to the RCBS powder die assembly that holds the Uniflow... the only reason being Hornady makes these available as an orderable part (they run about $25) - whereas RCBS doesn't. You can still buy them from RCBS, but you have to call them, explain to them what you want, and go through a little more work. Me... I'm addicted to Amazon One-Click, so that's what I do
Anyhow... with each die plate set up with it's own powder die, appropriate powder expander in the die, and the appropriate spacer(*), they get adjusted to the proper depth to provide the correct amount of case mouth expansion. Once set up, they stay that way - and I simply move the Uniflow from die to die as needed (loosen thumb screw, disengage case-activated linkage, remove spring from powder die pin, remove measure). This takes literally 10-15 seconds to move the powder measure from one set of dies to the other. And, of course, the Uniflow is much more versatile and reliable than an Auto Disc... no one's ever had their Uniflow spill powder all over the place, and when also equipped with the micrometer stem, you get very precise adjustment of the powder volume.
For me, the fixed station #3 has become a dedicated powder check station. I installed a Dillon powder check system (simple installation - just drill a hole), and use that now for both pistol and rifle loading. I used to use RCBS lockout dies for pistol (they work great), and the RCBS powder check die for rifle (works OK - with some issues). However, the lockout dies are a little less sensitive to powder level, and the powder check die is a visual indicator only. The Dillon is a little more sensitive to powder levels, and has an audible alarm when something's not right. It's also faster to adjust to a particular powder charge. To me, it's the best of the three powder check systems out there.
Station #4 for me is typically a bullet feed station. I use an RCBS pistol bullet feeder for my high-volume pistol (9mm, .40, .45), and a Mr. Bulletfeeder for rifle (.223, .308, and .30-06). I only recently added the MBF to my set-up... had I started with that, I would have done all my calibers with that setup. It's a VASTLY superior product to either RCBS or Hornady bullet feeders.
* spacers for the Uniflow - when using a powder expander, it's also necessary to use the RCBS-provided spacer to sit between the powder expander and the Uniflow drop tube, due to the short height of most pistol cases. Without this spacer, you won't be able to lift the Uniflow high enough to dispense powder, let alone bottom out to force case mouth expansion. The problem is, RCBS only includes one of these spacers with their kits. You can call them and get more, I'm sure... but that takes time. I've found that two 3/8-16 nuts are just about perfect. I take two of these, spin them onto the end of a long 3/8" bolt, lock the two nuts together (so they won't move on you), and knock off the corners with a bench grinder, until they just slip in to the lower powder die assembly. Then, remove them from the bolt, chuck them in a vise, and drill out the centers a little over 3/8" (just enough to remove all evidence of threads - so the inside is nice and smooth). Viola... custom Uniflow spacers.
