Hi FunSiteMaker, I'm directory owner myself for many years and wouldn't suggest you to start general one at that point, as Google is trying to fight with directories as there are too many abuse in this field. You can see thousands of small directories which have 3 links in total and doesn't contribute anything to the web overall.
The only good reason to start directory is starting niche directory which would only concentrate on specific sites. Than you don't have a problem with marketing it also as you'll be able to exchange links with some sites in the field you're specializing. Later if your directory become good resource people will link to it themselves.
The only advice isn't demand from sites to place reciprocal links for submission, I believe it's unfair and doesn't attract good sites to your directory.