Hello and welcome to GOY
Gardeners World mag (May edition) have done an article on growing Clematis in pots . They say the large flowered 'Niobe' (dark red) Keith Richardson is purple/pink or the deep purple 'Bonanza will do well.
If you cannot get a copy I could cut out and send you the article

if you want a container garden, suggest you get a good book for help and advice - one I'd recommend is The Contained Garden by Kenneth Beckett - it's available on Amazon still I believe. This book contains lists of suitable container specimens, info about the merits of different containers, and how to continue to manage your potted garden. But I can tell you straightaway that Magnolia is not a good subject for pot growing.