With regard to getting your watering right I've found that it's best to have
seed trays sitting in a tray with a little water in the bottom. You have to
adjust the water level depending on the depth of the seed tray, seeds planted,
compost type, etc. However, once you've found your water level, you can set up
an 'automatic' watering system to keep this level constant. All it takes is an
inverted bottle full of water with a nick cut out of the top to allow water
out/air in when the water level in the tray drops below the optimum level.
I've actually gone away for two weeks in mid-summer and left my plants to the
mercy of this system, and it works. I'm sure I'm not alone though.

Dave.