curtisa

The template ring is usually an accessory supplied by the manufacturer of the router that screws into the base. A metal cylinder protrudes from the base allowing it follow the edge of an object, and the router bit pokes through the cylinder to cut the workpiece. There are universal template rings offered by third party companies that are supposed to fit most makes of router. Do a search on 'router bushing ring' or 'router bushing guide'. Only bother with Perspex if you can get it cheaply. I get mine from the junkyard recycling shop. Sometimes it masquerades as other things - the piece I used to make the jig in those pics was a shelf from some kind of shop display. Cutting the slot itself, and working Perspex in general can be tricky. MDF works just as well, as @old_picker shows, and is easier to cut. The only disadvantages are that it's not transparent so it can be difficult to line up on the neck, and that it isn't as hard-wearing. If it were me, for a one-off or first attempt I'd go the cheapest route and just do something along the lines of the second link in my earlier post - ride the side of the router along some kind of straight-edged reference, such as some kind of metal extrusion or the factory-cut edge of a piece of MDF.

I use Timbermate all the time. Occasionally it needs a couple of coats/sandbacks to fill all the pores properly, but otherwise it works well, sands well.

Logo! Built like a boss.

Piece of Perspex with a slot cut up the middle. Router has the template ring installed that rides inside the slot: Here's a lower-tech alternative: http://www.bluestoneguitars.com.au/html/Craigs_Bent_Sides_Semi-Hollow.html#50

Also consider the trade-off as to which end of the neck you place the truss rod access with a rod like that one. Placing it at the nut means that you don't have to remove the neck or most of the strings to make adjustments. Placing it at the heel may be easier to execute from a construction point of view, but you'll either need to allow clearance behind the neck within the body to fit an allen key, or remove the neck every time you need to tweak the truss rod.

I'd just run a slightly larger router bit up the last inch or so of the neck to allow for the truss rod adjuster clearance. I can't see any real reason why the retention of an extra handful of cubic millimetres of neck would justify reaming the adjuster access like Stewmac suggest.