How many domain names do i need? Marketing, Resume, Blog, various businesses?

I have 2 websites up each with their own domain name inspirationcookies.com and lowcostplants.biz.
I own 1 more name.
For my personal webpage then should I get another name- and another for my blog?
can I have my personal page hosted on hostgator then get a subdomain and use wordpress for my blog and have the subdomain as the name for the blog?
If I am going to use a page as a resume site to get jobs should I keep it seperate from my personal stuff?
Are there any cheaper ways to go for getting good domain names than the major institutions?
If I am going to be signing up for forums, newsgroups, etc. and answering questions with the motivation of signing off with my website which website do i use- a chief website for myself with the others linked to it or a link directly to my business site?

Each website and domain name should be content specific. Jamming all of your different ideas into one website will be confusing to both human visitors and the search engines.