Bracing should be done as two cross-braces, one-third the way up and one-third the way down. Of course, you can never over brace. Additional braces like Shane did and/or window braces like Bill suggests won't hurt. Some even use a constrained layer to damp the box or glue random blocks or panels on the baffle interiors to break up panel resonances. There comes a point of diminishing returns, but the minimum should be a pair of cross-braces.

Use R11 or R13 insulation and span one side, the top and the front baffle, up to the woofer cutout hole. Also attach a sheet to each brace that completely spans the cross-section. It will look like you've broken the cabinet into three sections. Bass will go right through the insulation but it will trap midrange frequencies up, which is just exactly what we want.

The amplifier connection panel is included with the kit. It requires a 2-7/8" x 2-1/4" cutout on the back in a convenient place. The crossover is wired into the cable assemblies, so you can "plug and play" when you get them. The crossover components aren't so heavy that they can't just hang off the drivers, but you could also wire tie them to a cross-brace or attach them to a panel with silicon adhesive.