There are a variety of ways of obtaining the links that you need, and you should use them all.  However, I want to focus your attention on one of the most important of the link building methods, article marketing. 

There are several ways in which article marketing can improve your SEO.  First, if you do it properly, article marketing allows you to collect inbound links from a variety of sites that publish your content, and many of the websites will be from unique IP addresses, which is meaningful to algorithms of the major search engines.  Next, with content syndication, unlike some other methods of getting external links, you get to decide the exact anchor (linking) text for each link.  Third, this process is economically efficient and relatively simple to implement, particularly because of the accessibility of software to facilitate article marketing.

I write and spin about fifteeen article each week so that I really end up with the equivalent of hundreds of unique articles that I distribute to several article directories (for further distribution) or distribute directly to individual websites to which I have access.  I am able to reach that level of productivity because of two essential memberships that I maintain.

One of the sites of which I am a member provides a free article spinner tool, available to anyone.  When you first register to use the high quality spinner, you will also receive a free trial membership to an amazing directory submission service that will distribute a unique version of each of your articles to literally hundreds of article directories.

My other membership is to a service that also has a built-in article spinner, but this system require membership to use the entire system rather that breaking the system into parts.  The important difference with this system is that, rather than distributing unique versions of the article to directories, those article are spun and the distributed directly to websites. 

I maintain memberships in both, because both have their distinct advantages.  However, I can belong to both for a monthly fee that is less than I pay for a decent dinner for two in my home town.  Consequently, a combination of the two is what I would recommend for use in the SEO efforts for your mini-sites, with an added benefit of almost immediately increasing traffic.