Yeah, don't power it with the 3w SET amp.
In seriousness, though, when you are measuring the panels, measure three times, then cut precisely. Use Medium Density Fiberboard (MDF), and follow the plans exactly. MDF is wodely accepted as the best material for making speaker cabinets because it is very acoustically inert. Use the recommended thickness. You can find it at both Lowe's and Home Depot stores. Air leaks are your worst enemy. Use the glue-and-screw method at the cabinet edges. A good glue is Titebond brand. First glue and clamp (big clamps, obviously - they make these things that go on the ends of threaded galvanized pipe and work like clamps, I think they are called pipe clamps), then put in the screws. You can put the screws in before the glue has dried (but wait about 30 minutes), and this frees up the clamps for other things. Once you first clamp the edges together there will be lots of glue that comes out. Wipe this up, because I don't think it sands off very easily. Flush-mount the tweeter and midrange drivers. Cut the hole for the driver in the baffle (fancy term for the front panel). Drop in the driver and trace its outline. Keep the inside edge of the pencil as vertical as possible to track the driver edge as accurately as possible. Set a rabbeting bit on your router to the depth of the edge of the driver so that when you drop in the driver the top edge of the driver will be even with the baffle surface. Remove the driver from the hole before you start, obviously. First, (VERY CAREFULLY) follow the inside edge of the line you drew around each driver. Then, rout out the rest. Using a router on MDF makes a lot of very fine dust (MDF is, after all, a wood fiber composite material, not actual wood but wood fibers in an adhesive matrix) so be ready. You may want a dust mask, and you will probably want goggles or glasses. GO SLOW or else you'll probably make a mistake. I know from experience that the adrenaline really gets going from the noise of the router motor and the pressure of the situation, but take it a little at a time and be as accurate as you can. No one will see the mistakes except you, but you can be your own harshest critic. As far as woofer wire, use at least 12-gauge oxygen-free copper wire on the big woofers, and use nice wire on the midranges and tweeters.
Enjoy your speakers. Perhaps someday I'll have enough of an income to afford a VMPS kit. (I'm a poor college student.)