Experienced Affiliates, please help in my attempt at mini sites?

I want to try something different that I have not yet done, which is creating affiliate sites or blogs solely to promote other people's products. I promote products on my main site, but would like to venture out into other niches using min sites (or blogs), using more targeted sites, try finding the "right" product, keyword research, testing sales or opt-in page, etc.

So - for anyone who is experienced in this - Do you have multiple sites in various niches or are the niches all related? How long does it generally take you to put a campaign together for an affiliate product? Like, how long to choose a product, do kw research, then how long do you take to build traffic? Are you building traffic while split-testing or do you build traffic first then split test? And do you ever consider a site "done?" Like, when do you go on to try another site?

Sorry if I sound like an excited kid in a candy store, there is just so much to put together and I have wanted to try this for some time. I have researched the forum and found many ideas on how people do this - but have not found a post that tells me how long to expect to work on the various aspects of a site like this.

Thank you.
Cindy P.