Clematis? General information from Clematis growers?

I have bought three plug plants (Crystal Fountain, Empress and Josephine) and I want to know what to expect as I have not grown Clematis before. Plug plants in the UK are tiny - only a few leaves and a bit of root. I planted them in a pot in February and now they are about as long as my arm and the stem is about the width of a ball point pen inner tube - i.e. very thin. I was hoping to cover a small four foot frame by the summer, but these plants look very skinny so I don' t know if this will work. They also don't have anything to grip with yet, so I can't see how I can put them on the frame to get them going. Previously I have grown Sweet Peas and Morning Glory on the frame, but will the Clematis die out by the end of the summer or will it come back again the next year if I leave it (or do I need to do anything to it to make it come back)? Thanks!