If your woodworking energy is flagging, I'd hesitate to advise you to launch into a CNC-building project. But if you have a lot of enthusiasm for building things out of metal, and the skills and equipment to do it with, then it might be worth considering. Check out as many build threads on this site as you can manage; let other people's struggles inform your own. In general, you should strive for maximum rigidity; this - or the lack of it - will be immediately apparent in your cut quality. Build the frame before shopping around for electrical and electronic parts; things can change in the middle of a build, and you don't want to be stuck with motors and drivers that limit its performance. Also, there's a lot to learn about all this stuff, and giving yourself more time to learn it is a good thing.
On the other hand, it might make more sense to look around for a good deal on a used CNC router, rather than try to build one from scratch. Many brands have forums where people try to sell their used machines; it's also worth checking your local Craigslist or used machinery dealers. There's usually enough work to do in upgrading and maintaining a machine to satisfy most of us. If you're doing this to accelerate your woodworking projects, machine building would be a sidetrack, although it can be an interesting one.