No idea how long they take, but it seems quick compared to, say, courgettes. You'll see them as tiny little "proto-cucumbers" behind the flower, and you can watch them as they get larger. Depending on which variety you're growing they could look more or less like the shop ones, or they could be shorter or have prickles. But once you've eaten your own, shop cucumbers just don't hold an attraction any more.

Trellis - I don't know. Peas and beans need a good bit of sun to flower well. You could consider hybrid blackberries (eg tayberry) which in my experience do all right in partial shade. They are vigorous and need a lot of space. But they crop well, and it's a high value crop, so you feel quite smug as you fill basins full of fruit.