Hi caper, I wish you luck, and keep us posted! I noticed your thread at AVS too. If value is the main thing, I'd look into the Tuba HT designed by Fitzmaurice. It's really big though, however there are two sizes to choose from. I believe you pay $15 for plans. Its super high efficiency means you can buy a modest amp and still bring your house down.
Since not only do you have help, but expert help, don't limit yourself to "simpler" kits.
Going with a plate amp is personal preference I suppose, and my preference is to use an outboard amp with the intention of running speaker wire instead of an interconnect.
IMO, Neutrik Speakon connections are the way to go, both at the sub and at amp. Cheap, super beefy, super easy to connect/disconnect, super secure. I recommend calling them as plate and cable plug, not male/female because they are "opposite" from what we are used to. I also recommend the type where you can use a screwdriver to secure the wires, but that's just me.