I think you got a lot of good info here. Some other suggestions are:
Two groups very interested in your product are govt. works depts. and
schools. This should be included in your target audiences. In order for
school personnel to access your site, it will need to be rated(ie. safesurf, etc.).
You may want to think about banner ads and hard print ads as well.
Banner ads on sites that deal with the administrative duties of education
as well as sites that deal with public works type endeavors. Think about
trading links with heavy industry equipment sites. Advertise in classifieds
for specific journals ie. K-12, NEA (believe me people at all levels of staff
read these). You may also want to consider banners and ads on urban oriented sites
as well urban oriented journals. Oh a hint for your free content...
put up a graffiti board for people who visit your site to write on :)
(I know this could get out of hand but you can allow a script for exclusion
of words, phrases, etc.)
hth,
Pat
good luck