How to connect stages in digital logic?
Pat yourself on the back! 

This conundrum is exactly why logic chips come in standardized "formats", such as "TTL-compatible" (it literally means "transistor-to-transistor logic"), CMOS standards (HC, HCT, ALVC, etc.) and so on. It's why we care about "open drain" versus "push/pull", and factors such as propagation delays and power consumption.

I think your next step is to learn about those standards, as well as realize that instead of using lots of CMOS transistors, you can get faster CMOS circuits by using standard 78-series/4000-series logic chips. Knowing how to use CMOS transistors is great; but in a large system, it becomes quite a job to manage them all.