I had a 40 watt power compact 10000k + one actinic.. it was a "smart lamp" system.. came with a little lunar light. I bought some legs and that worked really really well for my 10 gallon. I liked the light. Cheap diy? Well, I'm certain you can find a cheap power compact fixture on the selling forum.
As far as the clean up crew... I would go with like 10 cerith snails, and you could put a few blue leg hermits in there. If you find that they eat all the algae, all you have to do is drop in a little piece of broccoli. They'll be all over it. No worries.
Don't watchmen goby get big? I can't remember. people seem to really enjoy their jawfish though. I'm getting one eventually.
Gotta cover your tank though.
My power sweep lasted two weeks, then shat the bed.
I started on a ten gallon nano. Great fun. =)
If you could hook up a sump, it will save you some room in the tank. I had 25 lbs of live rock to help with filtration in mine.