I agree - the HD650 is excellent with the Crack w/Speedball.
If you're patient, don't mind following detailed instructions, and don't have shaky hands, you should be fine. I had very minimal soldering experience and what I did do previously I had actually done wrong (with bad technique). But watch a couple of YouTube videos, practice on a few bits of spare wire, and you should be fine.
The fun part is you can finish the wood base and metal top however you'd like - so each Crack looks a bit different (unless you don't finish them at all, which is an option). And plenty of aftermarket upgrade options (like upgraded output caps, stepped attenuator, etc), though all I did was the Speedball kit. And plenty of tube rolling options to change the sound signature and make it look even cooler.
If you don't want to take it on, keep an eye out on the FS forums. They pop up every once in a while, usually for less than it would cost to have Bottlehead assemble it for you.