In a perfect world, an oscilloscope and a frequency generator are nice-to-haves. Not necessary, but nice to have.

Definitely a good soldering station. Doesn't have to be the most expensive, just good temp control and able to accept the right tips.

Check Peterson's site at diyrecordingequipment.com - not only can you see some of the build journals in his blog, but some helpful tips on starting out. And if you have any interest in the 500/51x platform, the CP5 preamp he sells is fantastic sounding, easy-to-build and accepts the DIYRE colour modules. I'm not on his payroll - just think that the space they occupy makes it much easier for fledgling DIYers to get in the mix.