I think the real "secret" is the right mix I think. Contextual links from content are great, but vary it. Contextual, a footer here, a sidebar/widget there, image link, banner link that looks like a real ad, "designed by" link on a contact or imprint page. Same for the sites, nothing wrong with wordpress, but there are a bunch of free CMS, hompage construction kits/services and even some old fashioned looking pure HTML site isn't wrong. Harder to manage than a single CMS solution, but worth it.
There is no law that a PBN must be a blog, just because of the B in PBN. In some PBNs, we e.g. have one site that just has text like "We are sorry, but for [whatever reason] we were forced to close down [old site name] after [domain age] years. Thanks to all [customers/visitors/clients/members] who stayed till the end, you can still reach us via [
[email protected], real, forwarder to trash], but can't accept any new [requests/orders]. We recommend [moneysite keyword links] in case you require a reliable [type of service] in [location]". Make it longer, add the history of the company, so basically a "farewell page", static HTML, one external link. Just a basic example, you get the idea, being a little creative won't hurt. The more variety, the more natural it looks, not just for humans, for Google, too.