I used a Digitrax Zephyr on my N scale layout when I decided to try DCC many moons ago. I took it with me when I changed to HO scale, and have been very happy with it. It will operate 3 or4 sound equipped HO locomotives at once, several of mine have the P2 installed. If and when you decide you have outgrown it, you can use it on the layout as an extra cab as well as a booster along with any other Digitrax system.
There are other systems out there as good, but I have had most of my experience with Digitrax, so that is what I am most familiar with. Most people can recommend what they know.
You're never too old to do something stupid.