When I do my routing I use a hand router and a wooden jig I constructed for the guide to run in. As far as measurements, for my blue swords I give a 1/2" allowance on each side, and use a "
core box" routing bit to route the channel. You can use a regular guide without a jig, but I find that it moves too much, and any screw-up in the routing makes the fry essentially useless.
Regardless of what you use, be sure that you don't compress the foam when you clamp it down, or you will route deeper than you need, and ruin the channel.
Hope that helps,
-Thurat-