If you have made one SE submission that's all that is needed.
I don't worry about search engine or directory submission.
Create a website that is easy to use and "inviting" to the viewer.
Offer worthwhile content.
Navigation is important.
The visitor shouldn't be scratching his/her head wondering what they are doing on your site
Everyone talks about "website/affiliate marketing" but before the Internet gained popularity "regular marketing principles" existed -- put those ideas to good use.
I believe internal links help.
If I create separate sites that are related, I have them link to each other: what do others think about linking across one's own sites?
If the layout is good, the content is good, and the title is catchy other people will link to the sites.