Homebrew PCBs

Electronics are a new area of interest for me (my skills lean toward 
mechanical design and fabrication, although I'm relatively 
comfortable with programming). A CNC project has forced me to dive 
head on into this world, and I'm in need of some tips to start out.

For example, I have a need to route the output of my drives on the 
basis of a three-position switch: e.g. "Off | Mill | Lathe". 
When "Mill" is selected, one group of output terminals become "live", 
when "Lathe" is selected, a different group becomes live.
I could almost handle this if all outputs were 5V TTL signals. 
Unfortunately, only 7 of the 9 are. The other two drive the motor at 
up to 80VDC @ 20A. This is clearly beyond simple signal switching, 
and I don't have the experience in power circuit design to figure out 
how to proceed.

Another, perhaps simpler puzzler for me is how to take a 17VDC, 4A 
unregulated signal and produce both a 5VDC & 12VDC regulated signal 
from it. Presumably, it's a matter of finding suitable voltage 
regulator ICs, but even approaching a simple circuit like this 
completely solo has me a little nervous.

I realize this forum might not be the right place to post such 
questions, so what is the appropriate place? While I'm open to book 
suggestions (and am plowing through a ton right now), I really 
appreciate the human interaction and practical advice that are best 
found on forums. Any suggestions? Are there professionals out there 
who offer design services for simple stuff like this at reasonable 
prices?

Thanks in advance for any tidbits you're able to throw my way.