Yes, it's blackhat. I think my fiverr linkwheels are what killed my main sites in April.

Depending on the "wheel". But honestly I prefer not to do a link wheel. Link pyramids seems to work much better.

Link pyramids and link wheels arrived from the same idea. If link wheel is blackhat then link pyramid is also blackhat. Both of those are created to give link juice to the money site. But they does not work for every site. Some sites have got great ranking through these, on the other hand some sites were effected by these.

Depends on your content if your content is good than Link well is good

Yes for sure it is a black hat technique.Although link pyramid works on the same strategy but it is more complex to recognize the main site from where link is travelling through the sites.

this is black hat technique,now Google is more effective after panda and penguin and harm our site but link pyramids can be useful for our seo.

Yes link wheel is considered as black hat SEO technique. But it depends on the complexity of the link wheel. If search engine can't recognize your link wheel than it can generate good results. And if search engine recognize link wheel that its red signal for your site.