controlling 120v devices through a relay?

You can use a smaller relay to trigger a larger one. But for interfacing TTL it is common practice to use a transistor to operate a 12vdc coil for example while triggering with 5V or less.

Also install a diode across the coil to clamp the inductive voltage generated by the relays coil. The diode is installed backwards with respect to the polarity applied to the coil. The diode is thereby biased to not conduct when voltage is applied to the coil. But whe the voltage is removed the induced voltage will conduct through the diode

Sure it's possible. Your local Radio Shack could fix you right up. Of course, the more relevant factor is not the voltage, but the current. Be sure to choose a relay with contacts that are rated to handle the expected current load at that voltage. As for the wiring, I wouldn't make a pc board, I'd get a socket or just solder to the terminals. Good luck!

Almost any 5 volt relay will handle 120 volts, you can buy them at Radio Shack. You will need to be very careful with connections because 5 volt relays are often small with connections close together. You will want to insulate the terminals with the 120 volt. I use silicone adhesive to make a rubbery coating. Liquid electrical tape is also available.