How many linked sites per ip should I be using? Say I have a network of 25-30 niche related sites what would be the most cost effective number of servers to use without spending too much?
(1) If the sites all bring unique content and interlink I don't see it being a problem honestly. I use to have a bunch of mini sites that did the same thing. The problem happens when people try to take shortcuts and start scraping content and throwing them on 400 blogs and interlinking them. It makes sense for you to interlink your own networks so should be no harm in that. If you find yourself writing unique content or somehow paying for it and the rankings don't increase or you've been penalized then resort to multiple C class ips.