Incorporate as much organic matter as you can into your clay and you'll be able to grow virtually anything. It will be the most fertile there is and roses will love it.
Perfect. Clay is great stuff providing you tie your boot laces good and tight in the wet.
Clay is a great constituent in soil as long as there is not too much of it. Unfortunately on some sites builders leave you clay subsoil or leave you a thin veneer of topsoil.
You will get plenty of advice to dig in lots of organic matter. As a no dig gardener I would suggest you add lots of organic matter to the surface!
Clay isn't bad, it can be hard work though. At times I curse it like today where I've spent most of the afternoon in a wet sloppy mess cementing in a post.. but come the summer when everything is growing, I'm not going to be complaining about being on clay.