If everything is working on the 4000 you basically have four software options, but only three that are viable. Those scanners usually shipped with a dongle for Aurora, which is a really horrible piece of crap. No color management and 8 bit output only. Trident is the best scanning app to drive any Howtek (or Aztek) but it was never updated for OSX, and runs on Mac OS9.2.2. The Windows version never really had the bugs worked out. Aztek's DPL does work, but has perhaps the worst interface I've ever seen and does not perform up to the level of Trident, no matter what Aztek claims. Silverfast will drive the scanner and is probably the least expensive option. You can download a trial version to see how that might work. A new Trident dongle runs about a grand from Colorbyte unless you can find someone selling a dongle for less.
The 4000 is the slowest drum scanner Howtek made and you have to make sure you have the version that had the upgrade that drastically reduced shadow noise. I don't remember what that was called, only that it exists. Evan at Aztek would be able to talk you through what you need to know.
It is good to know that Aztek is still servicing Howteks and that you can still get parts. PMTs do gradually wear out but you can replace them yourself with Hamamatsu 931B tubes directly from Hamamatsu.
As has been previously noted in this thread, you absolutely need a mounting station. If your new scanner doesn't come with one, they do show up on e-Bay once in a while and some prepress resale houses sometimes have them as well.
One of the things that you will have almost no information about is the history of the drum itself. It's important to know if it's ever been polished or resurfaced, because if it has and the surface has not been re-annealed, there's a real good chance that Kami scanning fluid could set you up for crazing of the plexi drum. Without knowing the specifics, I would would use a mounting gel and not Kami, no matter how enticing Kami might be. I've used Kami for the past fourteen years with no ill effect, but none of my drums have ever been polished or resurfaced. A new or even refurbished drum can be between one and two grand!
You'll need mounting gel/fluid, DuPont C-42 4mil overlay, and special mounting tape that doesn't come off with the mounting fluid. Then practice.
I spent about a solid month when I got my first drum (a Howtek 4500) way back when - mostly learning how to mount with no bubbles but more learning to get the most out of the software. I ended up giving Colorbyte so much useful feedback that they designated me their chief beta tester. I only wish I could have gotten them to make the jump to OSX. Oh well. Old Macs are really cheap now and I keep three of them around that can run the scanners.