The variety most commonly seen is 'Vossii' and this has the longest flowers, reaching lengths of 60cm . Although poisonous the particular variety 'Vossii' produces very few seeds in each pod (once the flowers finish) so I wouldn't worry about that.
Laburnums thrive in well drained soil, so in very wet gardens new plants have a history of just rotting and dying, so choose a sight in the garden where it doesn't puddle and where you can see it in the early summer when its at its best.
Laburnums are spreading trees, reaching heights of around 25' with a 25' spread on mature trees- when they're young they grow quite upright, but with age they start to spread out...you should be able to pick these up now in any good garden centre like here on Gardening Expresss website