<sigh> Here we go again.
Half the people here are using "PBN" to describe PUBLIC blog networks, where you buy posts on existing networks which sell to all comers.
The other half are using "PBN" to describe PRIVATE blog networks, which only have YOUR posts and links on them.
Good PUBLIC blog networks still work, but are taken down much more frequently than they used to be.
Good PRIVATE blog networks work like a charm (in conjunction with other link building), but their effectiveness and longevity depends on whether they're properly built to be hidden and, um......PRIVATE. Some PRIVATE blog networks were taken down this fall, which doesn't mean that PBNs don't work - it means the ones which were taken down didn't work because they weren't built and hidden properly.
Michlap, you forgot to include the "starting" part.
Most of the players have easily over a hundred after they get the ball rolling.
Don't you think having only single site/single owner site liked to multi PBN's (20+) is wont give a footprint
There isn't such a thing ''to being paranoid'' in this industry. If you are in to it - ''hide and seek'' or ''seek AND hide'' is what needs to be done. So, I would go for one site per host ,If I where you, or made sure that they are not near by shared hosting, the same IP c-block, accessed from the same e-mail (no gmail obviously ,so, proxies are must) and haven't used Google Analytic etc. Google products in general.
Good Luck!