Gosh, that's a tall order unless funds are not going to be a problem.
First, you need the engines with decoders, or decoders to add to engines that don't currently have them installed. You can get good prices on bulk deals of Digitrax decoders, as an example, but if you can't install your own, you can expect to pay between $20-40 per unit, depending on the work that has to be done to get the decoders inside the shells, and who is doing the work.
However, to get closer to answering your question, the systems generally handle more engines than two or three people can operate safely. You will need a fully computerized operating system to run more than three engines at a time in the vast majority of cases. That means even more decoder to operate the turnouts for routing all these moving trains.
The big issue is the amperage that you will need to meet the demands of each decoder and its slaved devices, be they lights, motors, or other devices such as turnouts and other stationary decoders....and we shouldn't forget any signalling and detection circuitry, plus and power reversing requirements if you have any reversing sections of track (loops or wye's, turntables that are not automatically reversing, etc.).
Then, if you want some sound systems on board the odd engine, or all of them, now you are getting into some serious power demand.
Count on approximately 0.5 amps for each working engine with a sound system activated. This is only a rough figure for computing your nominal power requirements. Some engines will draw a bit more, older stuff you get off ebay may require up to 0.7 amps. Many newer engines with sound systems draw as little as 0.3 amps when working fairly hard dragging cars up grades.
For safety, in order to keep the voltage at nominal values throughout the track plan, a system of a bus, boosters, power districts, and sets of feeder wires directly attached to the rails, will require some detailed planning, particularly for short management. Shorts with decoders are not a good thing, so all DCC systems are good at detecting shorts. They get inefficient as the voltage drops and the resultant signal to noise ratio drops. Eventually, at the far reaches of poorly power planned layouts, they won't recognize a short and the wires will glow in the dark. At the same time, your decoders will begin to let the magic smoke out of them.
The smoke cannot be contained and readministered. It's a one way deal.
So, now we have introduced the requirement for a lot of wire, connectors, and now boosters and more power supplies to keep the signal high throughout the trackplan.
Does that help to give you an idea of your challenges?
