Or, Duck Dodgers in the 51st Megahertz and beyond!

I'm interested in beginning to work with circuitry again, and would love some advice. I've dealt with analog, discrete things in the past. And on the formal side, I've studied a fair bit (for a college dropout) of EE/CE/CS. But I've no idea how to put the two together.

I know things change once you start dealing with higher frequency circuits. But how does one reasonably prototype boards? I've always been very incremental in how I do things - start with a minimum implementation, test it, and then embellish. Sending away for manufacture and paying tooling fees doesn't seem well suited to that. Do I just need to design a complete board on paper, and hope i got it all right?

More specifically: Where can I not reliably test without a PCB? Where might the practical threshold be where you *need* a dedicated ground (or power) plane? 30MHz? 60MHz? It depends? (I know I can print two layer boards at home, thus the concern for needing more layers.) Equally, where do I need to switch to surface mount over discrete packages?

Many thanks,
Douglas