It's a lot easier to make one domain earn £500 per week than it is to make 100 domains each earn £5 week.
The multiple domain approach seems a good one in theory however once you start doing this you realise that your time is being absorbed in the maintainance of the domains (mail, server setup, template setup etc) and not on the revenue generation.
It's a much better (requiring discipline) approach to build one site, promote it and then move on to the next. After twelve months you should have three sites all earning a few hundred a month. At the end of year two you are close to giving up the day job.
Of course I generalise and I haven't visited here in a while and there are sure to be peeps saying they can do it in 24 hours or shorter time frame.
People who have huge domain portfolios make their money from some nice type in traffic in the main. Simply owning domain names does not neccessarily give you the traffic to work with.
Build the site and then spend all your time submitting to the free directories. Here's a good start list
http://info.vilesilencer.com