Relevance will be passed but very little juice and very little trust.
Boost will be minimal. Even if you let them age still not much better.
However, it is possible to get aged web 2.0 with links just like regular domains. You should consider that.
I had trouble ranking for anything with slightly higher competition using web 2.0 network. And that was back in the day, can't image now.
However, since you are on the budget, go for it. Start with lower competition keywords. You can even power it up with tier 2 links they should take it (don't...
I don't know any resource that covers this topic specifically.
It is quite simple though. When you mention a fact, event etc you can cite a source.
This source should ideally not be your competitor, be popular in your niche and cover the pic well. Attributes mentioned before apply.
If they don't advertise publicly and their overall OBL is reasonable (don't make themselves obvious link farm) it is almost impossible to tell the link is paid. It's just regular editorial from outside look.
Are you referring to authority sites linking?
First of all, don't do Wikipedia.
Authority sites in your niche should be well known but also do not compete for the same keywords. They usually have lot of traffic, links, high stats like DR and pop up for searches all over the place.