sure, we like almost the exact same plants! and i live just south of London. I have just bought an alocasia calidora off ebay and i'm currently filling my tropical greenhouse(that's how i get my plants through the winter). I also wrap up some of my treeferns and bananas. I have plenty to trade, specially looking for any amorphophallus apart from konjac, strange musa/ensete, alocasias (nice big ones) colocasias, xanthosomas and anything with huge leaves that grows tall!

What a a well thought out landscape and lovely collection of plants. I so love your sidewalk planting - so much more interesting than a lawn. I think your Sasaella will be fine, so many plants are wrongly zoned anyway. I grow Sasaella albostriata and it is perfectly hardy for me. From the looks of the perennial plants you are growing, there really doesn't seem to be any zone difference at all between Zone 5 and Zone 3.

It looks like nodosum to me - while I freely admit to not knowing all the geranium. I've grown g. nodosum Svelte Lilac for years in dry shade. A little bit coarse looking without any care at all but still has its own charm.

Although they're not native to me I grow a little pot filled with hosta, fern, and blue geranium in full shade. It started blooming a month ago and looks lovely in that dark corner. I also grow them under blackberry with varegated Solomon's seal. Those only get winter sun so no flowers. But the leaves are evergreen here so its green in the winter when the berries and Solomon are gone. These geranium would grow under your ferns as they don't get tall so I think a spot where you can enjoy them is best.