Xanax sounds good.
I have a DCS100 myself. It's very nice. You don't really need to add anything to it other than a power supply. But there are a few things I'd suggest.
The first thing you need, since it's not included, is a power supply (Digitrax recommends their PS514). Anything that outputs 5A of AC at 12-20VAC or DC at 12-28VDC will work, but ideally for N-scale something around 14-15VDC (or 15-16 VAC) with 50+ Watts will do. An old laptop power supply, if it's large enough, is ideal.
I strongly recommend using a computer program and a Loconet-to-USB adapter to program decoders. Using the throttle's keyboard gets old fast.
You can either have a separate programming track, or use a DPDT toggle to connect one isolated part of the layout to either the normal output or the programming output (which eliminates the need to take the train off the layout). But the track needs to be short enough that you can position one car over it in a train that has multiple decoders (presuming you have such). I actually do my programming completely separate from the layout, since I had an old Zephyr I could put on my work table. That's connected to a test loop for running and a short length of track for programming.
It's probably a good idea to get a programming track power booster for the programming track. It's not required unless you have sound decoders, but Digitrax command stations tend to have under-powered programming tracks. The Digitrax PR2 will do the job (although I've never used one). The more common ones are the
PowerPax (which I used on my HO layout) and the
SoundTrax PBT-100. So far I haven't needed one for my N-scale trains, but I still have my PowerPax on the shelf if I do.
The PR3 is useful if you want to load sound files into a Digitrax decoder, and also works as a computer interface. But if you just want a computer interface, I think the
Locobuffer-USB is better.
Software depends on your computer. There are other threads discussing software on the board. I use JMRI, but it's far from the best (it's free, and runs on my Mac, and reasonably easy to use).
The other thing you may want is an
RRampMeter, which can be used in a variety of ways to measure current and voltage on a DCC system; it's an essential debugging tool. I use the version II, but you might want the version III as it can work even with very low track voltage (I sometimes regret not getting that one).
A good digital multimeter (for checking input power, and resistance) is a very handy tool. If you buy one, don't go cheap, you'll only annoy yourself. Among other things I use mine to find poor unijoiners (resistance >5 ohms between two connected track segments is an indication the unijoiner should be replaced); over time they get bent and/or dirty and make poorer contact.
Finally, if you're doing much Loconet, buy a spool of six-conductor flat phone cable and a phone jack (RJ11) crimping tool (a good one; your hands will thank you) so you can make your own cables to length and not pay outrageous sums for pre-made ones.
For the layout, I think a PM42 (or any other DCC circuit breaker, you could used just one for the whole layout) is a good investment. Set to some low amperage (like 2A) when used with a 5A command station and on a "fast" trip speed, and it will protect your trains from shorts that could otherwise melt them. Cheap insurance.
Depending on the layout you may also need a circuit breaker that can be wired as an auto-reverser (if you have any track that loops back on itself, or a wye). That would be dedicated to the track that loops back on itself, so another circuit breaker (or another output of the PM42) would be needed for the rest of the layout.
Also consider getting stationary decoders to control your turnouts, so you can throw them from the throttle. The Digitrax DS64 works well for Kato Unitrack switches (and reportedly for Tomix also).
I strongly recommend reading
Wiring for DCC before doing any layout wiring, in particular the
Track Wiring section.
