Yeah, DIY is probably more enjoyable to me than sitting back and enjoying my handywork, I've always gotta have a project.. my next one might be a DIY wave box LOL.. just not sure I like the idea of a big box in my DT ;-)
I can't really suggest anything specific for your cube because I don't know what you're looking for, or the restrictions that you have regarding space, do you need it to dim, what kind of color temp are you looking for... the list goes on ;-)
Im slowly working on a "LED Guide" thread that will have a lot of basic info as to how (in my opinion / experience) to light a tank with LEDs, not just the basics of you need x,y,z, more like a synopsis of how it all comes together and how to apply the basics. I hope to have it done soon and it might be able to help answer some questions like yours.
As for the soldering iron, I strongly suggest getting something that has temperature control, not just wattage control. I picked up a TENMA temperature controlled unit on ebay (refurb or new i couldnt quite tell) for only $60 and love it. It's so much better than the piece of crap radio shack one I used to use.