don't let the domains you own control what you decide to do. working at something you enjoy or marketing sites you like is important. also IMO creating a site to fit a domain is the opposite of what works.

if i were starting with my existing webmaster experience, i wouldn't start a site - i'd start a network - which, btw, is what i'm currently doing. if i were starting a site without webmaster experience, i would start a blog.

but i also don't start off by buying a domain or domains. i start off by considering what niche or niches i want to promote or what site or sites. OR i start with a concept. then i buy the domains. i have a newbie friend who recently bought 20 domains, and they're not bad domains but not one of them works for the project he's finally starting on.