How much traffic before advertising?

[th3g4me]

I have three blogs I have been working on. I am trying to get about 30-40 posts on each blog before I really try to trade links with anyone, or submit to blog directories.

These are 'How-to' and Technology blogs. Each blog has its own domain name and its own theme etc.

I was reading online that you should get a decent amount of traffic before you put any advertising on your blog yet none of these sites I have been looking at throw out a specific number. So I have a few questions for any of you bloggers out there.

What kind of traffic do you guys aim for before posting on those links, banners, or google ads?

Have you ever tried paying anyone at odesk or freelancer to write comments on your blogs or comment on other blogs to build up your back links?

Thanks in advance!