Cool, good luck, can't wait to see pics.
Isn't foam board fun to work with? It feels like being back in preschool playing with those big carboard blocks that have a brick pattern printed on them!

For a whole mess of seedlings, you need more light. A T12 shop light with 2 'cool white' or 'daylight' bulbs will run you no more than $15 at home depot and is good for a BUNCH of seedlings. It also does not get very hot.